You can find The Slave Pens dungeon within Zangarmarsh, Outland.
The coordinates are (50.1,40.5)
1. Mennu the Betrayer
/i Uses Lightning Bolt. Earthgrab Totem roots players. Stoneskin Totem reduces bosses melee damage taken by 50%. Healing Ward Heals him & lasts 30 sec. Nova Totem does fire damage to all nearby when destroyed or after 18 sec.
2. Rokmar the Crackler
/i Attacks a player with Grievous Wound dealing damage & healing. Slows a players melee & casting speed by 50%. Throws bolts of water inflicting frost damage to all nearby. Goes into Frenzy.
/i Deals ticking nature damage to all nearby. Sprays acid at a player & deals extra nature damage to all in front. Knocks back a player with Uppercut. Uses Cleave on a player inflicting damage to them & all nearby.