If Curator’s Ward is attached to a historic permanent you don’t control, you draw two cards when that permanent leaves the battlefield, not that permanent’s controller.

If you give hexproof to an opponent’s permanent, such as by enchanting it with Curator’s Ward, that player can still target that permanent, but you can’t.

A card, spell, or permanent is historic if it has the legendary supertype, the artifact card type, or the Saga subtype. Having two of those qualities doesn’t make an object more historic than another or provide an additional bonus—an object either is historic or it isn’t.