I have long struggled with the concept of God’s omniscience, especially when juxtaposed with the concept of human free will. I do believe that God is omniscient, but I am not sure what all omniscience entails. For example, I have 2 children. Does God know the name of my THIRD child? I submit that He does not, but that does not make him not omniscient. An omniscient being can only know that which CAN be known. My feeling (at least today) is that God gave man free will, and that He could make man’s free choices unknowable, by Him or anyone else. (Of course, in most cases God, and most of us, have a pretty good clue as to what a choice might be in a certain situation, but that is not the same as knowledge.)
God knows all that CAN be known. He does not know that which cannot be known. He is omniscient.
God has told us His name is I Am ... we struggle with meaning for concepts like ‘omniscient’, ‘omnipresent’, ‘omnipetant’ because we do not realize that dimension Time is a volume, not a linear expression as we perceive it limited as we are by His creating us this way for now ... As a volume, all of Time and Space are accessible to The Mind of God, and The Word of God, and The Power of God.
I stopped struggling with the concept of God's omniscience when I realized that understanding such a concept was impossible for finite beings to understand. I heard a phrase that stuck with me and may help. It's:
An eternal "being" would not be bound by time because He is outside of time and, in fact, God created time in the first place. So, though God already knows the end from the beginning - He "sees" all time simultaneously - He does not move everyone around like marionettes on a playhouse stage. Somehow - and this is the part that I don't think we can "get" - He knew everything before there was even anything. People ask all the time, if God knew how it all would turn out, why did he STILL go through with it? And the answer is partly found in Ephesians 2:7, "That in the ages to come he might shew the exceeding riches of his grace in his kindness toward us through Christ Jesus." It pleased God to STILL go through with it and ALL things work to HIS glory.
As to God only knowing what "can" be known, I disagree, I think His omniscience even goes as far as also knowing all the "what ifs" and I think when we face Christ at the judgment seat, we will also be shown those "what ifs". In spite of our free will choices, God's will WILL still be done on earth as it is in heaven. That part is the mystery that, among other things, we can only accept by faith. One day, however, it will make sense - when we have the mind of Christ - and we will "know even as we are known".