It should be at the maomer embassy. As the quest itself is just a quest to help you to the next objective ( The serpent lord is a quest you do on the way, but thats a side quest), it might also be that you can just go through serpents grotto (and do the serpent lord) and then walk to the next objective nord of the binding pools.
Through me you pass into the city of woe:
Through me you pass into eternal pain:
Through me among the people lost for aye.
Before the Storm is given by Treethane Fariel in the Thalmor Headquarters in Woodhearth (map). If you can't find her, you can skip it by going straight to Major Cirenwe at Seaside Sanctuary (map).