I've got this in the output of the "quests" command:

+ Answer an arial guard: 'I have some work for you, nod if you're interested'


I'm not positive, but I think the guard in question is in the Ruins of Delar-Tol. The quest initiated a long time ago, but I never actually nodded to him in order to get to the next step. Today I went back to work on it and couldn't get him to respond. Nodded to nobody in particular, nodded to the guard, said "Yes, I'm interested".

Possible its broken, or am I just talking to the wrong guard?

You are probably talking to the wrong guard, there are people who are completing this quest.