Siegesmith Stronghoof in Wintergrasp wants you to retrieve 10 Eternal Embers from Alliance players at the Cauldron of Flames.
Lok'tar, <name>! While the battle may have subsided, we must prepare to retake the fortress! Travel to the Cauldron of Flames in south eastern Wintergrasp and retrieve ten eternal embers.
The embers are mixed in with coal to fuel the Demolishers and Siege Engines.
We've heard reports of Alliance pigs collecting the embers all day. Slay them and take their embers! If they have already abandoned the area, then be prepared to fight the fire elementals there until you find some!