The immediate contents of the book upon the first inspection are all of the pages are blank. Either upon learning what the book does either through an arcana check (DC 11) or identify similar learning technique, the players can learn that:
    a player or NPC can focus on an empty page once per day (time: 1 action/ 1 bonus action during combat) and the page will fill in a language the holder understands, detailing a secret, rare fact, hidden knowledge (anything of the like) completely at random that it can fit within the single page. For example, this can range from anything to as small as the information of a couple they've never met having an affair, a random fact about a creature, or even the hidden location of a Sphinx's guarded treasure on rare occasion.

The book's randomness is up to the DM if they wish to keep the random fact truly random or use it as an occasional tool to give the player's helpful information. I would suggest keeping it consistently giving random facts and then occasionally helping players before they need it, but otherwise, in the game, the book works on a true randomness system. It is left to the DM to create or find random facts. They can be organized into tables corresponding with a d6, d20, or percentile dice to randomly show a fact, depending on how much the DM wants to work in making a table.