Private Doopy  

He's BEHIND the castle, near where the named skeleton spawns.

I have been back there 2 times recently to check for him but havent been able to catch him there yet .. Has the spot been changed or is he a trigger spawn ??

Doopy is a ghost, not a skeleton. A gnome ghost. He's outside the castle.

Doopy is a tiny little skeleton on the North side of the Gul'Thex Citadel. Getting to him can be kind of tricky if you are still aggro to owlbears and shrillers. The location given above is correct though. He is standing by a large stone marker.