An all-knowing being knows everything by definition. Knowing everything, it therefore knows that there is nothing that it does not know. If it did not know that it did not know everything, there would be a thing that it did not know, and so then, such a being would not be an omniscient being; rather, such a being would be a step below an omniscient being, who must, by definition, know everything, including that it does indeed know everything, perceiving with perfect understanding that all of the contents of its knowledge are not contradictory, including this thought element. Such a being would not even question its perfect knowledge, understanding that its perfect knowledge of all is entire and that there could neither exist nor subsist anything apart from this knowledge.
Your attempt at a contradiction was itself a contradiction. Thread ended.







