Omniscient is all knowing, nothing is unknown. Let me give you an example, imagine a teacher is omniscient meaning he knows all, and this teacher then decides to give a test to his students, now being omniscient he already knows who will fail and who will pass. He knows the result of the test already so why give it, people will then say the teacher was trying to give the students a chance, but there was never any chance of anyone that was supposed to fail to suddenly pass, if this happened the teacher would not know all and hence would not be omniscient. Now apply this to an all knowing God, by creating everyone he already knows who will go to hell and who will not, there is no chance of these people changing. So why create them, also why flood the earth in the story of Noah in anger when he knew what would happen when he created them. This contradicts so much about God.