The skyshard is found inside the largest area, in the northeastern part of the dungeon. This is an open area, full of Harpies and it requires caution. The collectible you search for is in the water, at the bottom of the waterfall.
Find and enter the dungeon.
Ilessan Tower Map Location.
It is next to the waterfall.
Exact location of the shard.
Sand Kingdom Moons - Super Mario Odyssey Power Moons