Agnis is an elderly woman located in Fort Greymoor. Nazir mentions something about how the Dragonborn's allegiance may matter in the killing. However, if the Civil War storyline has been completed, the Fort will be full of people from the Dragonborn's side, be it the Stormcloaks or the Imperials.
If the Dragonborn has not pursued the Civil War quest line and has no allegiance, the fort will be controlled by Bandits. According to Nazir's comment, their experience may vary.
Entering with hostiles holding the fort can be rough. Around the back of the fort is a small stream. There is a grate which can provide easy access into the prison area.
Fort Greymoor can be deserted when this contract is assigned, if, for example, all the Stormcloak soldiers have previously been killed. Agnis, however, will stay in the fort, making it easy to enter her room while she's sleeping and kill her with a silent arrow.
Agnis may, at certain times, be located in a small room far from anyone else, making killing her easier. At night only one guard will be awake and the room quite dark, so sneaking in is not difficult.
She is an interesting, if not clueless, character. If spoken to, she complains about cleaning up after everyone. If the Dragonborn chooses to tell Agnis to 'sleep, and embrace the Void', she says that she is too busy, asks what the Dragonborn is rambling on about and will not engage in conversation again. If she is told that she has 'cleaned her last room', she says that the Dragonborn is crazy because she has plenty more rooms to clean and ends the conversation.
After she is dead, return to Nazir, in the Sanctuary, for the reward.
Sleep now, old woman. Embrace the Void. "Sleep? I can't sleep now! There's too much to be done. And what's this Void you're rambling on about?"
You've cleaned your last room, servant. "But I have many more rooms to clean. Fort Greymoor is quite large, and rather filthy if I do say."
(Remain silent) "I swear, you people are an odd bunch. Please, just step aside, that I may return to my duties!"
I must kill the old woman Agnis, who serves as a servant in Fort Greymoor. I may use any means at my disposal. When I am done, I am to report back to Nazir at the Sanctuary and collect my reward.
Agnis is dead, and I have collected my reward from Nazir at the Sanctuary.
- Killing her (with Stormcloak/Imperial allegiance or if neutral) causes absolutely no stir among the guards or loss in standing with them.