The man has now become like one of us, knowing good and evil

1. I don't think word-studies provide the answer.

2. It's an interesting question who God's dialogue partner is in Gen 3:22. "Become like us". Perhaps it's the Spirit of God, who seems to be God's dialogue partner in Gen 1.

3. In my post I suggested that knowledge of good and evil refer to obedience or disobedience to God's command/prohibition:

http://triablogue.blogspot.com/2020/03/parsing-tree-of-knowledge.html

 Adam and Eve learn what evil is by simply doing what's forbidden. And it's a disappointing experience. There's no payoff. The only insight or enlightenment they gain is what it feels like to do what's forbidden. That's a very empty experience. They were hoping to get something out of it, but it's big letdown.

4. There has to be some kind of analogy between their experience and Gen 3:22. I'd say God already knows the consequences of obedience and disobedience, because he knows the future. He knows the aftermath of what Adam and Eve set in motion. 

5. A feature of human contentment or discontent is that we can be blissfully happy and contented so long as someone doesn't propose that there's something better we're missing out on. Simply planting that idea in the mind, that comparison with something hypothetically better, can foster discontent. The imagination does the rest. 

The mere suggestion that there's something better can foster the suspicion that we've been cheated. It isn't based on any actual tangible good they're aware of. It isn't based on any perceived good that's been withheld. Just the bare idea,

6. An example might be illicit teenage sex. The boy and girl are curious about what sex is like. They've been conditioned to believe there's nothing more enjoyable than sex, So they're in a big hurry to find out. They rush through it. As a result, they find sex is a big letdown. Natural goods can lose value if we approach them with false expectations. 

7. An example from classic literature would be Othello. Initially Othello and Desdemona are blissfully in love, but Iago seeks revenge. He knows that Desdemona is Otello's vulnerability. He plants in Othello's mind that Desdemona is having an affair with another man or simply in love with another man. Even though there's no evidence, the mere idea gnaws away at Othello. The groundless suspicion drives him insane jealousy.

The Tempter uses the tree of knowledge that way. Adam and Eve are happy until the Tempter suggests that God is holding back on them. They are getting second best. 

The mere idea is sufficient to make them dissatisfied with what they've got. They violate the prohibition to find out what they're missing. But all they discover is what it feels like to disobey. So now they have nothing to show for their transgression. They lost what they had without gaining anything in return, much less something better.