Deng is one of two small pandaren (presumably children) that can be found running around the perimeter of the Temple of Five Dawns in the center of the Wandering Isle. He and his friend, Cai, run in a large circle around the structure before descending the stairs leading to Mandori Village and then repeating their path.
Notes
He and Cai seem very impressed with players after they complete The Passion of Shen-zin Su, as revealed by their dialogue:
Cai says: Hey mister! Are you the one that brought back the fire spirit?
Deng says: Was he hot? I bet he was hot!
Cai says: Of course he was hot! Don't be dumb, Deng.
Deng says: I bet you're really strong, huh mister? You could probably kick that bridge right in half if you wanted to!
Cai says: Nut uh. Bet he could for sure kick you over that hill though! Hah!