I expect that at some date this will spark off a lively debate, but here are my thoughts and beliefs on it.
The biggest challenge that I see to this is separating omniscience from predestination and seeing the future. The basis of my belief stems from the fact that time is a man made invention. It is not a fourth dimension in which there is a physical reality. Man just made time up. For example, a day is 24 hours long, divided into 60 minute segments that are again separated into 60 second segments. This constitutes a photo period, (when the sun comes up to the time it sets and rises again) so a day is a photo period, or one rotation of the Earth. Where as Venus has one rotation every 243 Earth days. So their day has 5832 hours? Nope, time on earth is just something people decided on together, based on the Earth's revolutions around the sun. Way back in the day, it was mainly used to know when it was time to plant, so people did not starve. Seeds that were saved away from the food planted too early were killed if a hard freeze came. On lean years, the seed only had one chance, if it did not survive, there was no more to plant with, and people would starve in the winter. So knowing planting times, was very important, and where following the times of the year started. Not on any true scientific principle. Since time is a man made fiction, then their can be no flow of time into which the future actually exists, or is.
Omniscience by definition is knowing everything there IS to know. Since there is no future, it IS not, and cannot be known. Thus free will. Knowing the past is easy, these events have already taken place. Thus they ARE and can be known.
But what about prophecy? God says thing will happen, and they happen. Doesn't that mean he knows the future. No, it does not. It just means that he is so powerful, He can make anything happen anytime He wants. Let us put it in real terms that each of us will understand. I will make a prophecy that I will eat pizza in the future. A prophecy is a foretelling of events to come. They normally do not have any dates attached to them, meaning they can happen when God says, "OK, now is the time for such and such to happen, let it be done now." Through his power, they are done. Predestination is a little more specific, but still not definite. I have an appointment to go see the Doctor next Wednesday. That is a predestination. Now can unforeseen things happen that cause predestination to change dates. Absolutely. But since my wife wants me to go, you bet it is going to happen. So, prophecy and predestination are just ways of God stating his intentions.
This means that what we do now matters, because it actually has an effect on free will. Some will tell you that all is predetermined by God, because since he knows all, he knows the future. So no matter what you do, it has already been determined that it will happen. Sorry, no. The thing that I really like about the bible, is that again and again science proves it to be a correct and accurate statement of history. Science proves the bible. So since science can't prove time exists, it does not prove out this theory. But people will say that he predestined the "called out ones." OK, called out for what? Many people have many theories, but there is no real statement of who the called out ones were, are, or will be. So anyone eluding to this as a special thing that you should want, can not make it so, since God is the only one that can. If you were predestined before the beginning of the world, congratulations. Me I am not a called out one, just a servant of God.
So what does God know? Everything that was, is, and what he will do.