The Identify spell or Attuning the item will give them the command words.
Identify (spell)
"You choose one object that you must touch throughout the casting of the spell. If it is a magic item or some other magic-imbued object, you learn its properties and how to use them, whether it requires attunement to use, and how many charges it has, if any. You learn whether any spells are affecting the item and what they are. If the item was created by a spell, you learn which spell created it"
Attunement (DMG)
"Otherwise, at the end of the short rest, the creature gains an intuitive understanding of how to activate any magical properties of the item, including any necessary command words."
Not all items can be attuned. And my DM has ruled that Identify is not sufficient.
Then it is up to your DM to come up with ways to provide you with command words. Identify is supposed to fill that role in 5e.
If they aren't available through the standard methods then you are left with:
- research - go to libraries or other stores of arcane knowledge and see if you can find a description of the item
- investigation - is the command word coded onto the item itself? Does a close inspection of the decoration reveal letters?
- legend lore spell - this only works for legendary items but it could give you command words
- divination spell - might work - up to the DM
However, everything beyond identify and attunement is entirely up to the DM and their game. Try things and see if they work. 5e was designed to use Identify for this purpose and if your DM changes the rules then presumably they will provide some other way to discover the information. If not, just toss the item into the bottom of a lake and ignore it since it is useless :) ... that way no one else gets it and if you ever figure out how to use it you can go back for it.
Not all items can be attuned. And my DM has ruled that Identify is not sufficient.
You will need to ask the dm. RAW identify tell you how to use the magic item, which you can not if you do not know the command word. Your DM can rule differently but should let you know if and how you can.
I've ruled you need to pass an Arcana test as part of the Short Rest to identify and attune an item. Only needed the first time, and they can try again each rest. If they succeed once the whole party knows how to do it after that. I've also changed the DC on the skill check based on the rarity of the item. Just to give these more rare items a bit more aura of mystic. But an Identify spell will of course do the trick as well. But there is a pretty hefty component cost (at least at earlier levels), so this works out pretty good. Usually takes just a few tries anyhow
Some magic items are indistinguishable from their nonmagical counterparts, whereas other magic items display their magical nature conspicuously. Whatever a magic item’s appearance, handling the item is enough to give a character a sense that something is extraordinary about it. Discovering a magic item’s properties isn’t automatic, however.
The identify spell is the fastest way to reveal an item’s properties. Alternatively, a character can focus on one magic item during a short rest, while being in physical contact with the item. At the end of the rest, the character learns the item’s properties, as well as how to use them. Potions are an exception; a little taste is enough to tell the taster what the potion does.
Sometimes a magic item carries a clue to its properties. The command word to activate a ring might be etched in tiny letters inside it, or a feathered design might suggest that it’s a ring of feather falling.
Wearing or experimenting with an item can also offer hints about its properties. For example, if a character puts on a ring of jumping, you could say, “Your steps feel strangely springy.” Perhaps the character then jumps up and down to see what happens. You then say the character jumps unexpectedly high.
Variant: More Difficult Identification
If you prefer magic items to have a greater mystique, consider removing the ability to identify the properties of a magic item during a short rest, and require the identify spell, experimentation, or both to reveal what a magic item does.
Not all items can be attuned. And my DM has ruled that Identify is not sufficient.
DM may be sloppily telegraphing this item is some sort of Artifact, requiring legend lore. If they're not, your table needs a meta moment to determine what the DMs table rules for determining the function of magical items is so the game can stop playing the DM's "guess my mechanics" riddle. Otherwise the DM is just sandbagging or stone walling for unclear reasons. I mean, someone could make exploring a magic item a mini game but the DM has to be clear with something like "Nope, arcana and identify aren't working. The item has what appears to be script in an ancient language of a civilization upon whose ashes the Library of Answers is built" or "Nope, the item consists of a cube made up of a series of squares, nine to a side, the squares evenly distributed among six colors ... it appears the cube can be manipulated to adjust the distribution of colors over the cube...." stuff like that. Otherwise, they're just being unfair giving you literally nothing to play with to continue the game.
What spells or other methods can be used to figure out the command words for a magic item they find when they do not know it?
The Identify spell or Attuning the item will give them the command words.
Identify (spell)
"You choose one object that you must touch throughout the casting of the spell. If it is a magic item or some other magic-imbued object, you learn its properties and how to use them, whether it requires attunement to use, and how many charges it has, if any. You learn whether any spells are affecting the item and what they are. If the item was created by a spell, you learn which spell created it"
Attunement (DMG)
"Otherwise, at the end of the short rest, the creature gains an intuitive understanding of how to activate any magical properties of the item, including any necessary command words."
Not all items can be attuned. And my DM has ruled that Identify is not sufficient.
Then it is up to your DM to come up with ways to provide you with command words. Identify is supposed to fill that role in 5e.
If they aren't available through the standard methods then you are left with:
- research - go to libraries or other stores of arcane knowledge and see if you can find a description of the item
- investigation - is the command word coded onto the item itself? Does a close inspection of the decoration reveal letters?
- legend lore spell - this only works for legendary items but it could give you command words
- divination spell - might work - up to the DM
However, everything beyond identify and attunement is entirely up to the DM and their game. Try things and see if they work. 5e was designed to use Identify for this purpose and if your DM changes the rules then presumably they will provide some other way to discover the information. If not, just toss the item into the bottom of a lake and ignore it since it is useless :) ... that way no one else gets it and if you ever figure out how to use it you can go back for it.
Or doing as in Father Ted, just keep saying random words until you latch onto the correct command word.
You will need to ask the dm. RAW identify tell you how to use the magic item, which you can not if you do not know the command word. Your DM can rule differently but should let you know if and how you can.
I've ruled you need to pass an Arcana test as part of the Short Rest to identify and attune an item. Only needed the first time, and they can try again each rest. If they succeed once the whole party knows how to do it after that. I've also changed the DC on the skill check based on the rarity of the item. Just to give these more rare items a bit more aura of mystic. But an Identify spell will of course do the trick as well. But there is a pretty hefty component cost (at least at earlier levels), so this works out pretty good. Usually takes just a few tries anyhow
Identifying a Magic Item https://www.dndbeyond.com/sources/dmg/treasure#IdentifyingaMagicItem
Some magic items are indistinguishable from their nonmagical counterparts, whereas other magic items display their magical nature conspicuously. Whatever a magic item’s appearance, handling the item is enough to give a character a sense that something is extraordinary about it. Discovering a magic item’s properties isn’t automatic, however.
The identify spell is the fastest way to reveal an item’s properties. Alternatively, a character can focus on one magic item during a short rest, while being in physical contact with the item. At the end of the rest, the character learns the item’s properties, as well as how to use them. Potions are an exception; a little taste is enough to tell the taster what the potion does.
Sometimes a magic item carries a clue to its properties. The command word to activate a ring might be etched in tiny letters inside it, or a feathered design might suggest that it’s a ring of feather falling.
Wearing or experimenting with an item can also offer hints about its properties. For example, if a character puts on a ring of jumping, you could say, “Your steps feel strangely springy.” Perhaps the character then jumps up and down to see what happens. You then say the character jumps unexpectedly high.
Variant: More Difficult Identification
If you prefer magic items to have a greater mystique, consider removing the ability to identify the properties of a magic item during a short rest, and require the identify spell, experimentation, or both to reveal what a magic item does.
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DM may be sloppily telegraphing this item is some sort of Artifact, requiring legend lore. If they're not, your table needs a meta moment to determine what the DMs table rules for determining the function of magical items is so the game can stop playing the DM's "guess my mechanics" riddle. Otherwise the DM is just sandbagging or stone walling for unclear reasons. I mean, someone could make exploring a magic item a mini game but the DM has to be clear with something like "Nope, arcana and identify aren't working. The item has what appears to be script in an ancient language of a civilization upon whose ashes the Library of Answers is built" or "Nope, the item consists of a cube made up of a series of squares, nine to a side, the squares evenly distributed among six colors ... it appears the cube can be manipulated to adjust the distribution of colors over the cube...." stuff like that. Otherwise, they're just being unfair giving you literally nothing to play with to continue the game.
Jander Sunstar is the thinking person's Drizzt, fight me.