Tol Dagor stands as a well fortified thorn in this nation's side.
As you are no doubt aware, Ashvane has taken every opportunity she could to throw any opposition into those cells. Among those in the jail are members of the Alliance that arrived alongside you and Jaina.
We now have permission and the needed muscle to free them. Meet up with Taelia on the eastern shore of the island, find the overseer, and take his key. With it, we will have access to the weapon vault and cells.