Once you enter the dungeon, find and enter the portal in its southwestern part. I assume this portal takes you to the underground part of Bad Man’s Hallows. This is where our skyshard is located. Follow the path to your right. At the first intersection, go right. If you’ve been careful enough, you should spot the shard’s glow on your right side soon enough. It is located in a small gap. You have to jump toward it, in order to be able to grab it.
Enter Bad Man’s Hallows dungeon.
Use the portal found within the first area.
Turn right at this intersection.