If someone knows everything, they know things omnisciently.
This word is often used to talk about gods or other very powerful beings.
Examples:
The wizard knew everything omnisciently.
She spoke omnisciently about the ancient city.
The king ruled the land omnisciently.
The cat looked at me omnisciently, like it knew all my secrets.
The teacher seemed to know everything omnisciently, even things we hadn't learned yet.
He omnisciently predicted the future and it all came true.