Inside the Knife Ear Grotto solo dungeon. Follow the road east of Eidolon’s Hollow Wayshrine and when it stops, hug and travel along the northern river bank eastward until you see a stone building carved into a cliff. In the first big room you will see a metal bar door to your right. Skyshard is behind those doors, but you can’t open them from that side so you must go all the way around to get it.
The area where the dungeon entrance is located.
Knife Ear Grotto entrance marked on the map.
As you go through the whole dungeon and approach the exit door you’ll be able to pick up the collectible.
Sand Kingdom Moons - Super Mario Odyssey Power Moons