If you want to set your standard for knowledge this high ...

I'm not sure what you mean by a "standard for knowledge". What standard for knowledge do you think that I have proposed?

I would argue that you're claiming nothing counts as knowledge since no one has any way to tell how good their priors are independently of their priors.

You're talking about someone trying to determine whether their own beliefs count as knowledge. I already said that the question of "knowledge" dissolves in that case. All that they should care about are the probabilities that they assign to propositions. (I'm not sure whether you agree with me there or not.)

But you certainly can evaluate someone else's prior. I was trying to explain why "knowledge" becomes problematic in that situation. Do you disagree?