A: The person with Stolen Goods is the active player (i.e. it’s their turn), and they get to decide what they take from the other player when they give away the Stolen Goods to make this forced-trade. Of course, they can only trade with Keepers already on the table, not Keepers in the other player’s hand.

In the case of Garak (Star Trek: DS9 Fluxx) there are limitations on what Garak can be traded for (only Visitors / Other Personnel) but of course it’s still the active playing who is using their Garak Keeper to forcibly trade for another player’s applicable Keeper-in-play.