Guide:
Northwestern Shadowfen, northwest of Stormhold Wayshrine, west of Telvanni Acquisition Camp.
Inside the “Shrine of the Black Maw” solo dungeon. Start in Stormhold (it’s right next to Stormhold Wayshrine), and follow the road going west-northwest out of Stormhold. At the end of the road you will arrive at some shrine ruins, with the entrance to the dungeon located on the west side. The skyshard is located behind a wall at the eastern section of the southeastern hall.