Located in the Mukkir Nest on Dark Isle at 86.9N, 59.7E. He is at the bottom of the branch with Sclavus Acolytes of T'thuun. The branches with mukkir are dead ends.
Be sure to speak to the NPC for your faction before killing him, see Defeating Vaeshok for details.
In From Darkness, Light the xp was lowered from 310,000xp to 266,000xp and the level was changed from 195 to 200.