Speak with Zggi, the servant of Zardeth the Blackclaw, to claim your reward.
I hear Lord Wishock enjoyed his beverage.
You have served us well, <name>. The Warlocks of Stormwind will be able to practice our ways without disturbance, thanks to you. For your efforts, I have prepared a special gift for you. Speak with my servant, Zggi, and claim your reward.