I'm going for free smithing skill points and I've found out that doing the quest for Oengul (the smith in Windhelm) yields one as reward.

But the dialogue option that starts that misc quest isn't appearing.

It's a generic radiant quest to fetch an item from a dungeon; if you've already got a quest like that (for instance, finding Roggvir's Shield, or maybe Amren's Family Sword), you have to complete it before you can get the quest from him.