In the sidequest "Gnome trouble" you help the gnome Memble find a buried necklace in Gwydion Forest.
Memble tells you that his wife is sick and that the Wisp necklace might cure her. The necklace is buried somewhere in the forest and you help him look for it.
If you have the shovel you can dig it up. The necklace is near the mushrooms, south of Memble. Dig it up, and talk to Memble again to receive the reward of 2 Magic auras.