Yes. God necessarily knows things other than Himself because the divine power extends to other things by the very fact that it is the first effective cause of all things: and His existence as first effective cause is His own act of understanding.
His essence contains the similitude of things other than Himself.
The intellectual operation is specified by that intelligible form (which makes the intellect in act): and this is the image of the principal thing understood. But in God this is nothing but His own essence (in which all images of things are comprehended).