Just like the name says “Beneath the ruined aqueduct” head to the ruins in this area. There are rather tall stone structures – Aqueducts. The shard is conveniently hidden behind one of the Aqueduct pillars. Be ready for a bit of climbing. Aqueducts and shards go well together it seems, since are more than one in this area.
Sand Kingdom Moons - Super Mario Odyssey Power Moons