God can (and does) know everything; but, in the case of genuinely free-will choices, God could never predict what they would be, since, by definition, free-will, if such a thing existed, would have no determining factors. He could only know passively, by observing. This would mean that God would not be able to shape world history, since he could not determine what anyone would do, nor could he predict what anyone would do.There's nothing God can NOT know that has a truth value.
It's a nonsensical idea.
It's this kind of nonsense that leads some free-willers to dishonour God dreadfully, by teaching Open Theism.