Actually, the excerpt Twilight posted is from a guide for Ego Draconis and is now somewhat outdated.
Basically, fly into Broken Valley, head to the northeast corner (where the village used to be), and enter a teleporter in the northeastern-most chunk of the fortress. Kill Rayhun inside, loot the Amulet from the bag he drops, and return it to your Alchemist.
There are no anti-dragon barriers to disable in DKS.
EDIT: If you don't know how to get to the Valley now, look for the giant knight statue near the Grand Knight Shrine, then fly into the divide between the mountains directly north of it (maybe a bit northeast). It's quite obvious when you look for it. It'll take you back to Broken Valley, but be careful, because it's full of dragon defenses, and covered in poison gas (like Sentinel Island).
