Compel Soul
How the game itself explains this system.
Compel Soul allows you to extract information from the dead who still have a spark of soul within.
You can use Compel Soul with a Catalyst to extract specific memories. Catalysts are items of meaning to the deceased.
Compel Soul is a Witchcraft Ability and therefore accessible only in the Human form.
What the game tells you while you play
You can use Witchcraft Abilities via the Active Abilities tab.
Use Camera to hover over Compel Soul, then click Select to select it.