I have a device, the Demoniac Scryer, that can analyze fel magic. I would have you use the Scryer, but first... you must appease it. The Scryer, you see, has trapped within it a creature of vast intelligence and its needs are, shall we say, quite eccentric.
To appease the Scryer, you must kill orcs. Specifically, they must be Shattered Hand orcs -- the Scryer demands their souls.
Return to me when the souls are reaped. You will find the orcs north, and south, and surrounding... Hellfire Citadel.