I get the question a lot from non believers, "if God is all knowing and all powerful, then why did he create humans that he knew would disobey him and become evil and then having to kill them in the flood to cleanse the earth." How can I answer this question more effectively?

I can help you answer your question if God is all knowing and all powerful, then why did he create humans that he knew would disobey him, but first you need to help me to learn How to as soon as you can.
This is a question that a lot of people need to ask themselves, and I am sure that a lot of those who are asking this question right now. If they aren't, then they should start asking it soon.