Niklos's Master

This is one of those short side quests that doesn't involve any effort. All you do is speak with Niklos and either accept his offer to speak with his master or not. If you don't than this quest will appear in your Journal as finished. If you do it will disappear and be replaced with the Alatos and the Thieves' Guild quest entry.
However, if you don't accept Niklos's offer, it will remain in your journal as a finished quest even if you do eventually speak to Alatos and accept his quest.