MTG: whose graveyard?

If you look at the rules, they say "owner's graveyard" with such effects.

701.6. Destroy

701.6a To destroy a permanent, move it from the battlefield to its owner's graveyard.

701.14. Sacrifice

701.14a To sacrifice a permanent, its controller moves it from the battlefield directly to its owner's graveyard. A player can't sacrifice something that isn't a permanent, or something that's a permanent he or she doesn't control. Sacrificing a permanent doesn't destroy it, so regeneration or other effects that replace destruction can't affect this action.

704.5f If a creature has toughness 0 or less, it's put into its owner's graveyard. Regeneration can't replace this event.

704.5i If a planeswalker has loyalty 0, it's put into its owner's graveyard.

704.5j If two or more planeswalkers that share a planeswalker type are on the battlefield, all are put into their owners' graveyards. This is called the "planeswalker uniqueness rule."

704.5k If two or more legendary permanents with the same name are on the battlefield, all are put into their owners' graveyards. This is called the "legend rule." If only one of those permanents is legendary, this rule doesn't apply.

704.5m If two or more permanents have the supertype world, all except the one that has been a permanent with the world supertype on the battlefield for the shortest amount of time are put into their owners' graveyards. In the event of a tie for the shortest amount of time, all are put into their owners' graveyards. This is called the "world rule."

704.5n If an Aura is attached to an illegal object or player, or is not attached to an object or player, that Aura is put into its owner's graveyard.

For any edge cases:

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.

Let us define "owner" in MTG terms. Owner means whoever's deck/sideboard the card started the match in.

Whenever a card leaves play, it always goes to the applicable owner's zone (except for exile which is shared by both players) unless specifically stated otherwise. If the card is returned to the hand, it will always be the owner's hand, if the card is destroyed it always goes straight to the owner's graveyard.

Your opponent's.

All cards will go to their respective owner's graveyards.

Just because you control it doesn't mean you own it. Spells go to the graveyard is the layer who owned them.

Cards are always in their owner's zone, except for the Battlefield when control is changed.