Did God know beforehand that Adam and Eve would disobey him?
Yes, we know God knew beforehand because of Revelation 13:8 – the lamb was slain ‘before the foundations of the earth.’ God already had the plan in place before mankind was created. He told them not to eat the fruit so they would learn the importance of obedience, and that obeying God was an absolute requirement to life.
This gave us an important lesson in free will. God gave them the choice – eat and die; obey and live. Everyone who has ever lived will have to make this same choice in the kingdom and will be able to use Adam and Eve as a prime example.
Did Satan believe that eating the forbidden fruit will give knowledge of good and evil?
While we are not directly told what he believed, we can assume that from his time in the esteemed position as “Morning Star,” he saw firsthand God’s character and power. We can only assume he knew what he was saying when he promised Eve, “You will be like gods,” knowing that they would quickly find out that God was not lying about the consequences of their actions. Obviously they would get that knowledge of good and evil that they had not learned through previous experiences – they were too “new” to have understood the full implication and meaning of that phrase.