There are two copies of the key that Dro'Qosha knows of. The foreman, Dels Ravyn, has one of them. He keeps it always in a chain against his chest, close to the place where one would normally have a heart. Never takes it off. The other key belongs to Ulvo Hlaari. His room is on the left side of the Manor entrance hall. Dro'Qosha thinks the key might be there. Hlaari always works in the vaults, so the room is always empty. See for yourself.