This quest is not available in game.
Kill General Drakkisath.
Nefarian makes his domain further up the mountain in Blackwing Lair. Though there is a way in through the Upper Spire, we may bring a far larger force if we use the teleportation orb close by. However, we cannot teleport until we brand ourselves with a different orb.
Drakkisath, General of Nefarian's armies, personally guards this second orb. Eliminate him and secure his orb for our use. You will find him in the Spire Throne within the Upper Spire.