He can know anything He wants. And to assert that God must know everything would violate His absolute ability to do anything He wants.
It doesn't matter if god actually chooses to know everything or not. The fact that god can choose to know the future, which would fall under the category of knowing everything, requires that the future be unchangeable. Everything is predetermined. Therefore, free will does not exist. Also, god does not have the power to alter the future, which makes god a programmed robot. So much for omnipotence!