Once you’ve explored the area surrounding the house where you spoke with Professor Kenric, head east to the docks. Here you will find Fisherman Arvid being intimidated by some thugs. They will attack once you get close enough. After you’ve dealt with them, speak with Arvid to request use of his boat. He will ask you to seek permission from the Avvar leader, Svarah Sun-Hair, who can be found to the north east in Stone-Bear Hold. In your first conversation with her, you will be able to request use of the boat, which she will grant immediately.
Now that you have permission to use the boat, return to Arvid to inform him. You will find the boat at the end of the docks to the east. From the docks at Lady’s Rest, head south east to a hut where you’ll find a Fade Rift. Open it and speak with the spirit within to learn some new information about the old inquisitor. When you’re done, loot the body to advance the quest and earn the new ability Aegis of the Rift.
You can now return to Professor Kenric. If you return to the boat, you will have to fight a group of Hakkonites. If you’d rather not, just use the map to teleport to Basin Floor Camp, or run through the enemies to use the boat while ignoring them.