I am information.
~ The Great Intelligence when asked how he found out that the Doctor would turn to the dark side

Villains who are omniscient are capable of unlimited knowledge; they literally know anything and everything. Any villain in this category can and must be labeled as "All-Knowing" in the story that they are in.

Omniscient beings have imaginary and conceptual limits, however; most specifically, they cannot (unless certain ones have the abilities to do so) predict the future or read minds, meaning that their powers are restricted to what exists in their own thoughts and current space/time continuum.