Go up the steps into the ruin there and you should see the wooden doors that take you inside Troll’s Tootphick. Be careful of the Trolls inside since trolls regenerate their massive health pool and hit hard.
The skyshard is inside the small side room, in the northeastern part of the dungeon. This part of the dungeon has a cracked ceiling and the light is coming in from the outside.
Find and enter Troll’s Tootphick solo dungeon.
Troll’s Tootphick entrance map location.
If you are careful enough, the Troll won’t attack you.
Exact location of the shard.
Sand Kingdom Moons - Super Mario Odyssey Power Moons