The Spirits of the Dalish quest is available once you venture back to Arlathan Forest in Dragon Age: The Veilguard. You'll have to recruit Lucanis and venture to Docktown with Neve, but once you've done that, you can get the Unfamiliar Sense quest from Harding and the Winding Ways quest that sees you finding a route back to the forest through the crossroads.

Once back in Arlathan, you'll discover a restless spirit on a boat near to where you ventured to the blighted settlement earlier in the game. This quest involves finding five mementos, but it can be a little confusing knowing what to do after you've gathered them. Here I'll run you through each step of the Spirits of the Dalish quest.

Spirits of the Dalish memento locations

Once you speak to the spirit on the boat in Arlathan Forest, you'll be tasked with finding five clan mementos scattered around the region. This isn't too tricky since you get map markers and a search area for each, but I've included descriptions below, plus screenshots above of their locations on the map. You can collect these in any order:

• The first memento is on a wrecked boat in the middle of the river. Simply head along the shore by the falling rocks and hop along the stones to reach the boat. The body with the memento is just inside the wrecked cabin.
• The second memento is near the centre of the Shadowy Grove. You can access this by pulling the lever and heading through the gate near to the previous one. Search off to the side of the grove to find a broken eluvian—a big mirror—and some bodies with the memento just next to them.
• The third memento is inside a cave further along the shore from the first. As you get close, a floating rift will explode, opening the entrance. The memento is next to the pile of bodies inside, though you may have to defeat nearby enemies before you can pick it up.
• The fourth memento is in the west of the Shadowy Grove in a little clearing. Look for the people who have been turned into trees with the memento just next to them.
• The fifth memento is in Ruins Reach, to the south of the Shadowy Grove. Look for the body crushed under a boulder in the area with falling rocks to find the final memento.

Now you've gathered all five, you can head back to the spirit on the boat.

How to Perform the Rite

After speaking to the spirit again you'll get an objective saying that you need to “Perform the Rite” but aside from the hint that one of your current companions will give about a gesture, it's a little unclear what to do next. 

What you need to do is head up onto the cliff above the boat, behind where the owl statue is, and look for the differently coloured rock you can interact with using Harding's stone magic—or the knife if Harding isn't present. It's worth noting that you don't actually have to complete Harding's Unfamiliar Sense quest to do this. 

This will open up a secret area with a broken elven relic inside. Use Bellara's tinker ability with this—or again, the knife if Bellara isn't present—to open a portal. Now simply climb up onto the rock wall where the relic is and jump into the portal behind you. This transports you to a ritual site with the spirit where you can enshrine the mementos and lay the Dalish to rest, completing the quest.