Start at Fort Morvunskar Wayshrine, and follow the road going north. Just before you enter Fort Morvunskar, turn left, and go uphill. Soon, you will see a wooden door in a cliff. Skyshard is on the right side of the door, next to wooden crates and a wooden barrel. Quests in Fort Morvunskar lead to this skyshard as well.
Sand Kingdom Moons - Super Mario Odyssey Power Moons