In this case, a "Clerk" next to Tawenu ("Coming to terms" quest) in front of the Vailian Trading Company Headquarters in Queen's Berth. You can pickpocket him but apart from that he doesn't even say something generic like every other NPC usually does when you click on him. He also doesn't seem to move at all, as he's present at the same spot at night as well. There's also this Principi priest from earlier related bug reports here and here who's unusually unresponsive as well: