I see that Dan is following Sye’s tactic of asking “do you concede that an omnicient, omnipotent being could reveal something to us in such a way that we could be certain?” The answer, of course, is “no.” Now, I would like to clarify. Some people think that omnipotence requires the ability to do logically contradictory things like creating a square circle. Such a being is logically impossible and cannot exist. I will, therefore, only deal with the consideration of omnipotence as be the ability to do anything that is logically possible.
An omnipotent being could “reveal” a lie to someone and manipulate his mind so that he considered himself certain that the lie was true. He could further cast illusions that would make the lie seem true on any attempt at independent investigation. There would be no way to distinguish a true revelation from a false one. Therefore, there would be no actual certainty. Genuine certainly in the face of an omnipotent being is logically impossible. Even the omnipotent being cannot grant it.