How to beat a presupp at their own game

[Angrboda]

Very simple.   Atheism is "grounded" when we have no personal impetus to believe in gods.  That's all that the word means, so that's all that it takes.  

The same grounds for facts and knowledge that anyone else has, whatever those are - for better and for worse.  Adding or removing a divine friend has no effect on knowledge claims or their basis.

The same way we know things, if we know things, in a god-ed world.  To say that we know something is, like atheism or theism, primarily, a claim about ourselves - not a claim about a god.  In a godless or god-ed world we either know the thing, anything, or we do not.  Really, though, the questioner would have to be more specific.  You know your own name and what ice cream tastes like for reasons not at all similar to how you know that william lead the norman conquest.

Well, rather than arguing this point, ask them to explain what they mean by it.  How, in what way, is god the foundation of knowledge?  Who's knowledge?  What knowledge?  The foundation of knowledge of my own name or what ice cream tastes like?  You'll reach a point where..either what they have to say on the subject convinces you, or it does not..and then you have an even more specific answer for the very first question.

If a person has attempted and failed to convince you of a gods existence..they too are now part of the "grounding" of your atheism.  Congratulate them on a job well done.

Thanks for your reply! The answer I've heard from Darth is that whatever conforms to the mind of God is knowledge. You can only know that it is true if it conforms to the mind of God. And God has revealed himself through divine and special revelation in such a way that I know it cannot be false. He is also omniscient. This is his justication.

Katalepsis (Greek: κατάληψις, "grasping") in Stoic philosophy, meant comprehension. To the Stoic philosophers, katalepsis was an important premise regarding one's state of mind as it relates to grasping fundamental philosophical concepts, and it represents the Stoic solution to the problem of the criterion.

Stoicism
According to the Stoics, the mind is constantly being bombarded with impressions (phantasiai). (An impression arising from the mind was called a phantasma.) Some of these impressions are true and some false. Impressions are true when they are truly affirmed, false if they are wrongly affirmed, such as when one believes an oar dipped in the water to be broken because it appears so. When Orestes, in his madness, mistook Electra for a Fury, he had an impression both true and false: true inasmuch as he saw something, viz., Electra; false, inasmuch as Electra was not a Fury. Believing that the mind instinctively discriminated between real and false impressions, the Stoics said that one ought not to give credit to everything which is perceived, but only to those perceptions which contain some special mark of those things which appeared. Such a perception then was called a kataleptic phantasia (Greek: φαντασία καταληπτική), or comprehensible perception. The kataleptic phantasia is that which is impressed by an object which exists, and which is a copy of that object and can be produced by no other object.

Wikipedia || Katalepsis

One of the problems with this line of reasoning is that it leads to an infinite regress.

For example:

"I know that knowledge is what conforms to the mind of God."

"How do you know that you know that knowledge is what conforms to the mind of God?"

"I know because I know that my belief that knowing that knowledge is what conforms to the mind of God also conforms to the mind of God."

"And how do you know that that conforms to the mind of God as well?"

And so on. The point is that in order to know, one has to know that one knows, and in order to know that one knows, one has to know that one knows that one knows, and so on.