Guide:
Eastern Greenshade, just north of Marbruk, southeast of Falinesti Wayshrine.
Harridan’s Lair solo dungeon contains the shard. You can reach its entrance from north. This is an easy solo dungeon. Level 30-ish tigers in groups of maximum two are your only obstacle. Collectible is inside southeastern part of the cave. Bright glow from cave’s ceiling enhances the glow of the skyshard. In the next cave room, you can find Razorclaw, which is the mob you need to kill for dungeon’s completion.