The term "sacrifice" generally refers to a card's controller putting it into the graveyard due to an effect or to pay a cost. Traditionally, equip only happens to your own creature, but Ardenn made it possible to attach Wargear to another player's creature. How does the "sacrifice" work here, officially?
In general, the sacrifice will succeed only if Grafted Wargear and the permanent it was unattached to are controlled by the same player.
When Grafted Wargear becomes unattached from a permanent, the player who controlled Grafted Wargear at that time is the one who's asked to sacrifice that permanent (C.R. 608.2c, 113.8). However, if that player doesn't control that permanent, they can't sacrifice it this way so that there is no effect (C.R. 701.17a, 101.3).
In general, if you control Grafted Wargear and attach Grafted Wargear—
from a creature you control to some other creature, Grafted Wargear's triggered ability will trigger, since it was unattached from a creature, so that you must sacrifice the creature it was unattached to this way when the ability resolves (C.R. 701.3d).
from a creature you don't control to some other creature, Grafted Wargear's triggered ability will trigger, since it was unattached from a creature, but when it resolves, if you don't control the creature it was unattached to this way, you can't sacrifice the creature so nothing happens (C.R. 701.3d, 701.17a, 101.3).