This is the path you need to take to get to the shard. It is in north Hoarfrost Downs.
Map location of the start of the path.
Shard is slightly hidden behind a cave’s entrance. To the left is the named troll and behind the character in the screenshot above is the sick tree.
Exact location of the collectible shown on a zoomed in map.
Sand Kingdom Moons - Super Mario Odyssey Power Moons