Explosion => no quest, but hints (look at my manuscript link and later on listen to the smith talking to his imp in the lava forge)
Rum => you need the quest "Steal a book" from merchant Tully. Then Kegan (guard in front of Bram's hatch)will tell you about loving rum - and after you have the bottle take it => drops key.
Skull => did - wanted you to kill the Fergus (Torture master)
