Agnosticism should not be confused with Gnosticism. The two words both come from the Greek word 'know', but for different reasons.
The word agnosticism contains the prefix 'a-', which means 'not'. So, an agnostic does not know whether there is a God.
Gnosticism was a major, early branch of Christianity, in which the believers, or Gnostics, sought to 'know' the truth about God, not just to have blind faith. The early Gnostic schools no longer exist, but some believe that the Rosicrucians still follow some of the early Gnostic principles.
These are fine distinctions, but some philosophers define a range of beliefs: Thiest - certain that god exists. Weak thiest - acknowledges that one can't be certain, but believes. Agnostic - neither believes nor disbelieves. Weak atheist - acknowledges that one can't be certain, but disbelieves. Strong atheist - certain there is no god. As you can see, "weak atheists" hold the middle ground - in fact, most atheists are probably weak atheists - they acknowledge that certainty isn't possible, but it is very unlikely that god actually exists.
No, she is an agnostic.
The main difference between an agnostic theist and an agnostic atheist is that an agnostic theist believes in the existence of a higher power or deity but acknowledges that it cannot be proven, while an agnostic atheist does not believe in a higher power or deity and also acknowledges that it cannot be proven.
Yes, he describes himself as atheist or agnostic.
PewDiePie has not publicly disclosed his religious beliefs.
Probably agnostic/atheist
PewDiePie is an agnostic atheist.
I presume you mean, Richard Branson. He is an atheist.
"John is an atheist, which means he does not believe in the existence of any gods or deities."
Amy Thiest is 5' 4".
By definition, all humans are born agnostic atheists
She describes herself as an agnostic.