This is a quest that requires you to speak to this NPC at every Vestige you find him at. Miss one, and you will fail the quest. You can find him at the following locations

• Skyrest Bridge on the path to Pilgrim’s Perch.
• Pilgrim’s Perch / Forsaken Fen border
• Forsaken Fen / Fitzroy Gorge border (the vestige after the Fen’s beacon boss.)
• Path of Devotion (optional route from teh right tunnle before the bell boss in Belled Rise.)
• Manse of Hallowed Brothers
• Abbey of Hallowed Saints

If you make it this far, you will get the trophy after defeating Judge Cleric.

You can learn more about the Thehk-hir questline here.