Agnosticism and gnosticism are actually not so much about doubt, but whether it is possible to know.

An Agnostic says it’s not possible to know whether there is a god or not.

A Gnostic says it’s possible to know whether there is a god or not

An Atheist says they don’t believe a god exists

A Theist says they believe a god exists.

You can be an Agnostic Atheist. “I don’t believe in god, but I don’t think it can be proven god doesn’t exist.”

Or a Gnostic Atheist. “I don’t believe in a god, and I think we can prove God doesn’t exist.”

Or an Agnostic Theist. “I think God exists, but I don’t think we can prove it. You just have to believe”

Or a Gnostic Theist. “I think God exists, and I think we can find proof.”