Can the rod absorb cantrips?

What would say, 5 cantrips equal in terms of power absorbed, 1 level?

Can an ally cast cantrips at you all day to be absorbed and allow you nearly unlimited spell use?

This seem likely to be abused....anyone use this item?

Cantrips are treated as having a spell level of 0, for multiple purposes and in many scenarios. Highly likely to be the same here. 

"If you are a spellcaster holding the rod, you can convert energy stored in it into spell slots to cast spells you have prepared or know. "

Does this mean that a Wizard can cast any spell (or 5th level or less, anyways) he has in his spellbook without preparing them?  Aren't spells in his spellbook are considered "known".

No, spells in a spellbook are not "known".

Can this absorb Counterspell?

I don't think it would absorb counterspell.  This specifies that you need to be targeted by the spell, counterspell does not target the caster.

Can this absorb no-save spells like Power Word:Kill?

So long as the rod hasn't absorbed more than 41 points in it's life, I see no reason you couldn't absorb Power Word: Kill.

I don't know what this other guy is talkin bout, but for future folks lookin, yeah. Spells in your spell book are known. Even says right on the wizard page "Your spellbook is the repository of the wizard spells you know."

Counterspell targets a creature casting a spell. The rod absolutely can absorb it. 

It states prepared OR know.... basically if you “prepare” spells they must be prepared, if your the other type and have access to ALL your known spells at all times you “KNOW” them! 

pretty sure this is a perfect example of read into to understand type BS 

This would be stupid good for a warlock

Could I as a Wizard use Wish to make it so it can absorb "up to 50 levels and can continue to do so as long as the energy does not reach over 50 energy.." effectively just making it so it has a cap like staff of the Magi, but never loses its ability to absorb? or just Wish to give it's ability to create spells from its points of energy to Staff of the Magi instead of gaining energy each dawn, so really combining the best parts of the two staves with a wish? 

I guess so as long as your DM is ok with it

So does casting a spell using the reserves in the rod take levels out of the rod? Or once it gets to 50 can it never absorb anymore spells ever?

Yes depending on the spell slot the level is cast at it takes out that amount of points and yes if you don’t use any points and it gets to 50 it becomes useless 

Would be great if it recharged indefinitely. Still useful for a while, though!

Quote from Ampelos_The_Malevolent >>

Yes depending on the spell slot the level is cast at it takes out that amount of points

this is incorrect. in the item description it states that when you are attuned to the rod you know how much it has absorbed over it lifetime and how much it currently has stored. those are different values. the amount of absorbed magic is only ever increased, and CANNOT be decreased. the amount of magic currently stored is variable and can be increased—by absorbing more, or decreased—by expending it to cast spells.

so regardless of whether or not use use stored magic, the item will be unable to absorb any more magic at some point. after which, if the attuned user depletes the stored magic by using it to cast spells, the item becomes inert.

Quote from hostileeldritch >>

So does casting a spell using the reserves in the rod take levels out of the rod? Or once it gets to 50 can it never absorb anymore spells ever?

once it has absorbed 50 levels it cannot ever absorb any more. those levels of spells are still able to be used to cast spells though.

think of this item like sheets of paper. there are 50, initially blank (except for the 1d10 set upon finding). absorbing a spell fills a number of pages equal to the absorbed spell's level with arcane runes, glowing with power. these filled pages are able to be burned by the attuned caster, releasing their energy, which they shape into a spell of their choosing, up to 5 pages at a time can be used this way to generate the power necessary to cast spells up to 5th level. once the 50 pages are full they can never be empty again. once the 50 pages are burned they can never be written on again.

if you want an item that can be reused, look at https://www.dndbeyond.com/magic-items/staff-of-the-magi

Absorbing cantrips would be indefinite because a 0 level wouldn't count as a level in the rod but is still a spell?