This ability is unlocked if you spend 120 hours over a period of 12 days reading all of the Realms of Magic and have spent the time studying the nuances of its purview of magic. These books go into detail about all the schools of magic and dive into an exploration of the possibilities and theory of magic in great detail.
When 120 hours is spent, over 12 days, reading this series of books, your Intelligence, Wisdom, or Charisma increases by 2, and that Ability Score's maximum increases by 2 as well.