Player A plays Emissary of Grudges and chooses Player B.
Player C steals Emissary of Grudges with Mind Control. Can Player C look at the named player? Can they activate the ability and reveal the name if Player B targets them with something?
I'm getting thrown off by the phrasing of "Reveal the name you chose:". 'You' should refer to the creature's controller, but Player C didn't choose a name.