Where does a card that is recast with Rebound end up after resolution?
The card will go to the graveyard if you cast it from exile with Rebound.

When a spell represented by a card has finished resolving, then by default the card goes to its owner's graveyard. 


  608.2k As the final part of an instant or sorcery spell’s resolution, the spell is put into its owner’s graveyard. As the final part of an ability’s resolution, the ability is removed from the stack and ceases to exist.


Since Rebound only applies to a spell when you cast it from your hand, it does not apply when you cast it from exile, so it doesn't get exiled as it resolves. Since no other effect takes place, it goes to the graveyard as normal.