Unable to complte this quest
 

Uldum
Do the World a Favor

When you complete the quest you are prompted to click on the yellow ? to complete the quest but the yellow ? is never presented. Must turn off Carbonite to clear that quest, then turn Carbonite back on.

Has never worked.

You don't have to turn off Carbonite. If you run into the problem again, hit Alt+L to bring up the default quest window and complete it from there.