Ending an attunement and attuning to another object in the quickest way.

Quote from MaximusArael020 >>

If the attunement ends when you die, then the fastest way to do it would be to have someone kill your character and immediately Revivify.

 Ah yes, death as as shortcut (there are situations where this would save you time, but it requires wanting to switch 2+ items).

Quote from SmiteMakesRight_3_5 >>

Quote from Jayce_Danathar >> 

Since the item is an enspelled dagger, I do not know if casting Find Familiar as a Ritual (70m) without expending a charge of the item it is possible. 

You cannot cast the spell as a ritual since the enspelled weapon does not give you the spell as a prepared spell so you must use it as a standard spell with a 1-hour casting. A Thayan Spell Tattoo would allow it though. As far as I know, that is the only item that does.

 Slightly off topic, but am I correct in my understanding that casting Find Familar from an enspelled weapon does not require to burn the 10gp of incense indicated as material component?

Quote from Jayce_Danathar >>

Quote from SmiteMakesRight_3_5 >>

Quote from Jayce_Danathar >> 

Since the item is an enspelled dagger, I do not know if casting Find Familiar as a Ritual (70m) without expending a charge of the item it is possible. 

You cannot cast the spell as a ritual since the enspelled weapon does not give you the spell as a prepared spell so you must use it as a standard spell with a 1-hour casting. A Thayan Spell Tattoo would allow it though. As far as I know, that is the only item that does.

 Slightly off topic, but am I correct in my understanding that casting Find Familar from an enspelled weapon does not require to burn the 10gp of incense indicated as material component?

Correct. Spells cast from magic items don't have material (or verbal, or somatic) components unless the item description explicitly says they do (which Enspelled Weapon does not). This rule is easily missed as it's tucked away in the Dungeon Master's Guide chapter on Treasure.