In the quest, Wynne mentions that Aneirin went off to seek the Dalish. You can go to the Dalish camp in the Brecilian Outskirts to ask around about him, and Sarel, the storyteller, will give you more info. You'll eventually find Aneirin in the forest by himself. I found him nearby the hermit and the ruins. Make sure you bring Wynne with you to make the most out of the conversation.