Proof of the non existence of God
We will first assume that God exists and try to prove that God is not all knowing. So if God knows everything then this includes knowing all that has happened in the past and all that will happen in the future and this means knowing what our actions will be before we actually do them. This means however that we cannot have free will over our actions because if God knows what we will do before we actually do it, then it will happen anyway and means we do not have any choice in the matter. This doesn't prove that God is not all-knowing but means that either our sense of having freewill is an illusion or God does not know everything and therefore is not God.
We will assume for now that everything that exists is contained within the universe, including God. This means that everything must follow the laws of the universe, including God. But if God is subject the laws of the universe it means that God can not be all-powerful because God's power will be limited by the laws of the universe. Now you could say that God is not part of the universe, so let's assume that there are things which exist out side of the universe, there are now two possibilities. 1: that these things and the universe are contained in something else which is bigger, or contained in something else which is limitless, but are still subject to some sort of laws. If this is the case then God's power will still be limited by the laws that govern these other places and so cannot exist. The 2nd case is if these things outside of the universe follow no laws, this means there will be no laws to limit Gods power, it also means however that if there are no laws outside of the universe then everything outside of the universe is random because without any rules an entity cannot interact with another entity or with itself (so anything can happen when these things interact with each other or themselves). For example let's say that God wants to create a planet outside of the universe but because there are no laws anything might happen, God could instead make a giant bowl of cold custard with tins of baked beans inside with out meaning to, or just by thinking God could cease to exist. So in the 2nd case God's power is not limited by physical laws but is instead powerless.
So if there exists laws then Gods power must be limited and subject to these laws and if there are no laws then God is powerless, either way God is not all powerful which means that it is impossible for God to exist, instead only a very powerful life-form can exist.