To start this quest you should talk to The Watcher.
A warrior known only as 'The Watcher' has bid us to kill the Knight of Duna, who has been afflicted by a curse. He can be found within the Dwarf Temple.
The Watcher's Mercy
Related points of interest
Quest stages of The Watcher's Mercy
1. Knight Killed
Go to Duna's Sanctum and talk to Cursed Knight of Duna .You can try to persuade him (2 checks) or you can kill him.
The Knight of Duna is dead.
1.1. End
Report back to The Watcher. He will give you The Watcher's Amulet - it grants Guardian Angel skill.
The Watcher thanked us for our help, and rewarded us with a magical amulet.
1.1.1. Quest Reward
2. Close Left TNI
We have left the Nameless Isle, without fulfilling the Watchers' request.