You can find the shard on a small island in southeastern Elden Root. This small island has one road going into Elden Root and out of Elden Root toward southern Grahtwood. It really lives up to its name because of its location on a small island.
Find a small island in southeastern Elden Root, close to a road, next to a large tree and a stone structure…
…and you’ll find the collectible.
Elden Root collectible map location.
Sand Kingdom Moons - Super Mario Odyssey Power Moons