The path that takes you to the dungeon’s entrance is used by one Imperial female called Catina Garrana. She is the dungeon’s quest giver. Go down the path close to the main bridge, and in the lower area, you’ll spot a wooden bridge that will take you inside.
The exact spot where the Forsaken Citadel skyshard is, is in a part of the delve where two paths go one above the other. It is in the northwestern part, next to a room with lots of wooden tables, chairs, barrels… This is a room with four large central pillars. You can see the skyshard’s glow from the upper path, but you’ll need to jump into the hole to reach the lower path, where you can actually interact with it. The enemies you’ve picked up along the way won’t follow you down the hole – they’ll take another route instead, and you’ll be locked in combat until they reach you, hit you once, then change their minds and head back. Luckily, this won’t stop you from interacting with the shard. That’s the last shard on the list – have fun exploring the vast zones of Elder Scrolls Online.