This quest is not available in game.
King Jokkum at Dun Niffelem wants you to enter the Halls of Lightning and defeat Volkhan.
I shall speak plainly to you, little <race>. My people have not been the same since our ties with Thorim were severed.
As their leader, I wish nothing more than for their hearts to be mended and our friendship with the Stormlord to be renewed. In your defeat of Fjorn, a step has been taken down that path. I would have you bring us a step further...
In the Halls of Lightning, one even greater than Fjorn sits in opposition to our existence. Volkhan will not rest until either he, or we, are no more.