God.
Sounds like some kind of wise crack, I know, but it’s the only really correct answer. God is a simple being (or, rather, is Simple Being), so there is nothing compound in him, like a real distinction between His Nature and His Essence. If this weren’t so, if God were complex, then He would be made of parts, each of which would be less than the whole, which is infinite being. What is less than infinite is finite, but finite things added together can never equal infinity, no matter how great or how many those finite things may be.
Thus, divine nature is ultimately simply God Himself, just like the divine essence is God Himself, or just like the divine existence is God Himself, or the divine intellect is God Himself, or the divine will is God Himself, or divine goodness is God Himself, or divine power is God Himself, etc. etc. etc. Can we really comprehend this? No, it’s far too great and simple an idea for our puny brain neurons with their fleeting ion currents to make anything out of. But we can still know it’s true, in a sort of apophatic way. We can know God is not complex. Therefore we can know God is simple. We just can’t comprehend this simplicity.