You have to be in Townlong Steppes.
Do quests leading up to Terror of the Dread Wastes (http://www.wowhead.com/quest=30900) - pick up this quest.
1. Kill Norvakess (http://www.wowhead.com/npc=62324) that is needed for quest completed.
2. Abandon the quest.
3. Run halfway up the hill and the quest giver will spawn again after a few seconds.
4. Pick up the quest again
5. go to 1.
The mob has 3,256,512 hp. On my Frost Dk, I use approx 50secs - 1min10 sec to kill it. Depending on the burrow.
The mob has a 1 minute respawn timer.
The mob gives you 198.000 XP if you are rested at lvl 89. Dont know how much on level 88. Apparently, Battle Standard of coordination (http://www.wowhead.com/item=64402)bonus does apply.
If you are past this quest in you chain, I doubt it will work as its phased.