[If it's Nick, he'd most likely meet Jon in the Gray Room, so that's a decent place to start, though he has no idea about Dorian. He's met him, but doesn't really know him well enough.]

Alright, so it's likely Elias or Dorian, if he had some last minute guilt about not telling you. [Sounds like Jon.] I should be able to feel for the Eye and narrow it down from there, same way I can find you with the Lonely.

[The trick is that it's a big city and he doesn't know where to start.

Although...]

When I met with him a while ago, he picked the library as neutral ground. Might not be a bad idea to start there.