There is only one Monastery on the River Exe, so it is just a matter of searching the entire area. As you might expect, the clue is in the building that is the farthest from the river. Enter the door ...

This is one of three quests given to you upon completing On Borrowed Time. This quest can be found in Hemthorpe. Head to the teal objective marker on your map. When you arrive, speak to the seer.