Start in Riften and follow the road going north. Right across the watch tower, on the other side of the road, there is a huge rock formation consisting of one big and two slightly smaller cone-like rocks. The skyshard is right in the middle of the formation.
North of Riften Wayshrine, South of Fort Greenwall, about half way. It is on the West of the road across from a guard tower, among rocks.
Sand Kingdom Moons - Super Mario Odyssey Power Moons