This quest is not available in game.
Speak with Sage Truthseeker in Thunder Bluff.
Well <name>... we seem to be at an unfortunate impasse. We know what we need - the Plates of Uldum - but we have no idea where they might be. We will research this, and then devise a solid plan of attack. I have a couple ideas where to start looking; I have high hopes that soon, we'll be asking you to rejoin our efforts to discover the truth.
Sage Truthseeker needs to be informed on this, <name>; no doubt, he also wants to thank you personally for once again heeding the call.