Bring Verog's Head to Regthar Deathgate, west of the Crossroads.
The centaur Verog the Dervish wanders the Barrens, and will be difficult to find. But he is based at the centaur command tent at the Stagnant Oasis to the southeast. It may be possible to draw him to you.
Travel to the Stagnant Oasis to the southeast and attack centaur near the command tent. It will be dangerous, but if you can kill enough centaur then they should raise an alarm. And Verog will come.
Bring me his head and I will place it with Barak Kodobane's.