So you think when God said ' Do not eat of the tree', and Eve told the serpant 'we should not eat of the tree', Adam and Eve had no knowledge of Good and Evil?. If Eve had no knowledge of evil how did she know eating of the tree was evil, the wrong thing to do?. Until that time they were not evil but they still knew evil like God because it come through a command. So as Jesus knew evil but did not sin and was obedient.
'Do not eat of the tree'. That is knowledge of what is wrong and right through a command.
As soon as a command is given there is the knowledge of evil.
Scripture said they were given a commandment to not eat, that is all it says. They ate and their eyes were opened, Adam being created a living soul I believe at this point recieved something from "the sinner from the beginning," a nature. With that nature "the knowledge of good and evil" began to plague all humanity from that point on.
It took the cross to free mankind from that nature, we still deal with the knowledge of good and evil. To the unsaved they still have a sin-nature, you must be in Christ to be free of the old nature and free now to recieve the nature of God which is in Christ.
A late edit: the sin problem we face as believer's is soul-mind. When we talk about flesh that is basically mind given to body to work it's magic. The miracle was in spirit, a complete exchange was made at the cross and in us the moment we believe.
Oldman out, new man in, that's spirit.
There was some renewal in mind for some when they believed, but we are to be renewed in mind.
The process of mind renewal takes all that the Father has allowed in this world.
We learn, we grow through a process of mind renewal. Nothing exists if He doesn't want it too. Contrast is a great knowing process, oil and water, day and night, law and grace, old and new. Instructors, teachers the Father puts in a life to bring them to Christ, and then start a process of developing a son. The world is a schoolhouse, and in that schoolhouse are many classrooms, many teachers, it can be a hard road but the "the suffering of this present time is not worthy to be compared to the glory which shall be revealed in you."
Knowing the plan (glory) of God goes beyond understanding.