Found inside the “Forgotten Crypts” public dungeon. At the Quarantine Serk Wayshrine follow the road south. When you reach the crossroads follow the eastern path until you are about to cross a bridge. Instead of crossing, move along the northern river bank and you will see doors carved into a cliff which lead into the dungeon. Once inside, just follow the path and it will lead you to a crossroad where this skyshard is found. Be careful, this is a public dungeon with large (4+ NPC) groups so bring some friends along.
You can see the entrance to Forgotten Crypts above.
The location of the dungeon’s entrance on the world map.
Mid way through the dungeon you’ll come across the shard.
The location of this skyshard on the dungeon map.
Sand Kingdom Moons - Super Mario Odyssey Power Moons