Disenchanting breaks down magic items into the raw resources Enchanting needs to create scrolls and other enchanted goods.
In Night Harbor, the Disenchanting Trainer is tucked inside Vaclav’s Tower, reachable either by befriending an Enchanter with the Silver Key of Candor or by finding the tower yourself in the Elementalist District (look for the purple torches). In Faelindral, Disenchanter Gwendyl teaches the skill above the Inn, near Vaelyndir the Jewelcrafter. You’ll need a Disenchanting Cube, sold by Enchanting Supplies in Night Harbor or an enchanter in Faelindral.