If I were to cast Hijack on one of my opponent's creatures then, while that creature is under my control for the turn, I cast Blood Divination choosing to sacrifice the creature I took from him/her, does that creature go into my graveyard (since I control the permanent), or does it go into my opponent's graveyard?
This happened recently while playing with friends and we just decided to put it in the original owner's graveyard.
Because Magic has physical cards worth money, they go to some lengths to ensure your cards don't accidentally end up with another player. So there is NO way one of your cards ends up in another player's deck, hand or graveyard. (The other zones are shared.)
400.3. If an object would go to any library, graveyard, or hand other than its owner’s, it goes to its owner’s corresponding zone.
That said, things don't get that far in this situation. Sacrificing instructs you to place the card in its owner's graveyard.
701.16a To sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. [...]
There used to be an exception when playing for ante, but that doesn't exist anymore.
You put it to its owner's graveyard, so in this case it's your opponent's graveyard. Magic comprehensive rules define how you sacrifice a permanent:
701.16a To sacrifice a permanent, its controller moves it from the battlefield directly to its owner’s graveyard. (...)
