For this quest you need to destroy eggs. If you go into the sewers you'll find a number of these eggs near the undersewer entrance. These can be repeatedly destroyed in the following way:

1. Destroy the eggs
2. Do the following two times: go into the undersewers and then back up to the sewers.
3. Go back and destroy the eggs again.
4. Repeat as often as needed.

If anyone knows more about this, like who to bring the eggs to, please post about it. There is no in game quest as far as I can tell that refers to the eggs. Conversely there is a quest (The Strange Man)  that is in the sewers but never shows up in the Quest logs. Search Strange Man here for details.

Quest is given by Gnarus in The Lykeios after you have completed the main quest for this DLC. 

Reward was 2,912 gold at level 25.