Why can't God sin?

[Nobody]

you misunderstand what the "metric" of the knowledge of good and evil means. To be without sin does not mean one is automatically naive or unaware of complex emotional thought. The angels are without sin, and yet are fully aware of all the wickedness and evil in this world.

Adam and Eve weren't ashamed of their nakedness until after they ate of the fruit of the tree of knowledge.

It was then that they became consciously aware of their nudity and assumed an insecurity about that.
Prior to eating from the tree, they could not have possessed a consciousness of good an evil, when god told them to eat of the tree that bore the fruit of knowledge would make them like unto god in having that awareness.

Giving them orders not to eat of the fruit required they be cognizant of the parallels between obedience and disobedience, in order to elect to obey and comply with god's ordinance to abstain from the tree of knowledge and it's fruit. In order to give those commands god had to know they did not know what good or evil was in order to make an informed choice to obey or disobey him.

And then in the midst of that the cherubim that guarded paradise from satan, whom god let to be lord of the earth and who acts only by god's will, were removed from their guard post so that the satan gained entry into paradise when god is omnipresent?
And if god is omnipresent, after the eating of the fruit when Adam and Eve hid from god's presence, why is it that he had to call out and ask where they were? How could humans hide from god when he's omnipresent and omniscient?
And how could omni-benevolence relieve the cherubim from their posts in the exact same moment that then allowed his antithesis to enter into paradise and tempt the first humans to eat of the tree that could only have served as a temptation in the first place because god put it there?

When omniscience would have known exactly what was to transpire because a sovereign deity predestined eternity.