Inside the “Onkobra Kwama Mine” solo dungeon. Head southwest of Percolating Mire Wayshrine until you see a small hill next to a river bank. The entrance to the dungeon is from the river bank side. The skyshard is on the top of the wooden platform located in the eastern cave. You will have to kill the boss to get to the the collectible though.
Wooden door leading into the dungeon.
Onkobra Kwama Mine entrance location
Area where this skyshard is located.