This skyshard is hidden near the Giant’s Heart point of interest. In order to reach this place, leave Windhelm and follow the road going east. Leave the road when it turns north, and head east. You will soon see a big fire in front of a huge rock, and a few giants around it. The skyshard is next to a broken wooden wheel cart with a chest on it. This area is populated with giants but you will have no problem avoiding them.
Sand Kingdom Moons - Super Mario Odyssey Power Moons