This shard is found inside Wormroot Depths public dungeon. There are stone stairs that lead to the entrance of this dungeon. They start from the nearby main road. Collectible is in the corner of the first larger room you come across. As you go down the first stairs inside Wormroot Depths, turn right and you can notice it easily. Patrols of nearby creatures are rare, and should not worry you at all.
Stairs that lead to Wormroot Depths entrance.
The public dungeon entrance map location.
As you go down the first stairs inside this public dungeon, you can spot the shard in the corner of the room.
Sand Kingdom Moons - Super Mario Odyssey Power Moons