Circlet of Proficiency lets you copy a non-interactive skill in the common pool.
What is a non-interactive skill?
page 14 of the Rulebook. Bottom Center.
In the friendly game explanation, there is a section talking about NO INTERACTIVE SKILLS.
It gives a description. There is an icon of a Helmet (see rulebook for it) that designates the skills interactive. Each character has one in their skill tiles.
Goldyx is Source Freeze
Norowas is Prayer of Weather
Tovak is Mana Exploit
Arythea is Healing Ritual