In Assassin's Creed Valhalla you can come across Cairns that will give you extra points. This page of our guide has the locations of cairns in Jotunheim.
This cairn is in the northern part of the region, among the mountains.
It is a very simple task. Arrange the stones so that the entire structure breaks through the blue marking. You don't need to use all stones, four will be enough. To make the task easier, we marked them in the above picture.
This will give you an extra skill point.