Slay 15 Dark Iron Taskmasters and 15 Dark Iron Slavers. Return to Taskmaster Scrange in the Searing Gorge once you have accomplished this task.
Taskmaster Scrange is looking for a few good men and women to help 'cull the competition' in the Searing Gorge.
If you are interested in this position, venture out into the Searing Gorge and slaughter every Dark Iron Taskmaster and Dark Iron Slaver that you see.
Return to Taskmaster Scrange when your clothes are bloody enough.
You'll know when they're bloody enough so don't ask.