1-st part of the Assault: The Black Empire is pretty straightforward, just complete the objectives on the map.
[npc=153326] is located in the Vale of Eternal Blossoms and he is the final objective of the Assault: The Black Empire
He is underground and the entrance is near the huge statue south-west of the rare (You can see a statue on the map (top one near the The Golden Pagoda title))
/way 57.28 38.78 Vil'raxx cave entrance location
/way 80.98 28.43 Vil'raxx location
Vil'raxx location video: https://www.youtube.com/watch?v=h-HVbuhJFVA