This point becomes even more evident with the idea that god answers prayers. For prayer to work, that implies that god is willing to change events for a specific person. However, if god is willing to change events, then he cannot be all knowing. If he was all knowing, then he already knows how everything will turn out. Therefore, the prayer is pointless. It either coincides with what god always has planned or it does not. If it does coincide, then there was no need to pray because the outcome was already what you needed before you prayed for it. If it does not coincide, then praying is pointless because it never had a chance to change anything.
If prayer actually does change events, then god cannot be all knowing. If god is not all knowing, then he is not all powerful. Since the standard model of god says that he is all knowing and all powerful, then he cannot be answering prayer and changing events to something he did not already plan for.