Visit Gamlen Dragon Age II Guide

The quest giver: automatically after completing the main quest Demands of the Qun [Hightown - Hightown Square]

Step 1: Talk to Gamlen

You will get this quest automatically after completing the main quest Demands of the Qun and after meeting with Knight-Commander Meredith and First Enchanter Orsino in the [Hightown - Hightown Square] location (M3, 22). According to the information you got, you have to visit Gamlen. In order to do so travel to the [Lowtown] location. Being there head to the residential district and click on a door leading to the [Lowtown - Gamlen's House] location #1 (M12, 4). Talk to Gamlen #2 (M14, 4) touching upon longing for dead Leandra among others.