1. Either find the Pendant first in the cave
2. Talk to the two NPCs just outside the East Entrance to the Hollow City. I think if you talk to the NPCs first, you get a quest marker in the cave. But I usually wait until the cave is visited to do this.
Enjoy the game, life is what you really want to be worried about.
PakKat "Everything was going well, until I died"
Gary Gravestink "I am glad you died, I needed the help"
I know this is a bit late, but for others who happen across this thread searching as I did:
The pendant is no longer in the location shown in guides and videos - they predate the expansion of the delves to larger spaces. It is now found in the ground floor room in the upper left side of the map, right as you enter the room from the east.