Skyshard is inside Roots of Silvenar solo dungeon. There’s a small path that starts from a nearby river and an interestingly looking boat and leads to the dungeon entrance. It’s in the largest cave room, next to the pond, rather close to the dungeon entrance. It is hard to miss if you are inside this room, as its location in the middle of the area dominates the surroundings.
Find and enter Roots of Silvenar.
Roots of Silvenar entrance map location.
Among roots, fungus…
Next to the area marked as water.