On this page of the guide to Assassin's Creed Valhalla, you will find a detailed walkthrough of the quest called A Little Problem.
Reward for completing the mission: 5,100 XP, Man's Best Friend ability.
You will meet Knud in the longhouse. From your conversation with him, you will learn that there are children in trouble in the forest. Follow Knud deep into the forest.
When you arrive, you will find that the children are not in danger and just wanted to lure you to the place where they heard the howling of a wounded wolf. At a nearby pond you will find a wild boar - kill it and take the house key from its body. Enter the house and go underground.
Release the wolf from its cage and go outside. Talk to the children and then escort them to Ravensthorpe (you'll have to fight against the wolves along the way once), and the quest will be completed.