Just because you know something is possible doesn't mean you know it in the general sense of the word ''knowledge''. Knowledge is a justified true belief. As you can see U isn't known to be true (it's only possible) and so doesn't count as knowledge or something known. — TheMadFool
Aside, your definition of knowledge is highly suspect. I'll roll with it for now.
Modal facts about possibility, contigency, necessity, and impossibility are facts.Take a unicorn, a horse-like being with human cognitive abilities, a horn on its head, and magical powers. Unicorns are logically possible, as they are concievable and not self-contradictory. To use possible world semantics, there exists a possible world in which unicorns exist. This possible world does not have to be the actual world. Unicorns may not be contigent (actual), but they are possible. From this, we can list a number of things about unicorns. Unicorns:
1) are horse-like beings.
2) have horns.
3) have human cognitive abilities.
4) have magical powers.
5) are logically possible.
All these statements are true, per how I defined unicorns. Just because something is logically possible does not mean we cannot have justified true beliefs about it. Onto U. Assume U is true. U:
1) is something about which nothing can be known.
2) logically possible.
The first statement is true by the definition provided. The second statement, according to you, is true because there is nothing self-defeating about U. Therefore, in the same way I know about unicorns, I know facts about U. I can add another fact to the list of facts about U. U:
3) is something about which something is known.
The third statement contradicts the first statement. Therefore, U is logically impossible, as U is self-contradictory.
O can't check all universes, which I've shown is infinite, for the existence of U. So, O is NOT omniscient. If U exists then O is not omniscient. — TheMadFool
If the omniscient being is similiar to God, then the being does not need to search for any true statement. The being just knows it all already.