Philosoraptor

Arguably He would know by having designed the process. If not that, then by being able to watch lots of us go through death on both sides of the process.

God's knowledge is not like our own. He doesn't learn anything. His knowledge is perfect, and eternal, and pre-exists creation. Therefore, what happens to us in death and everything afterwards is an outworking of the perfect knowledge he had about those things "before" time.

God also knows what sin is, even though He himself has never sinned personally (and never could).

If you had read the Bible, you would know He DID die. Jesus Christ, though the SON of God IS God. When He was crucified, He died and spent three days in hell so we could be free from sin.

Why would god have sin in the first place could he not just instantly remove it if he was all good and powerful without making himself and other suffer ??

Jesus had to take on the sin of the world in order to pay the sin debt we could not pay ourselves. He had to be fully God and fully man in order to do this. We however can not do this because we are only mortal. If He decided to just remove the sin since yes, He is all good and powerful, He would not be able to accomplish the penance for our sin. By making 1 suffer, He saved everyone from the consequences of our mistakes. He was entirely perfect, but by putting on all the sin of past, present and future mistakes He succeeded where we had failed.