He knows, therefore, He is. If He cannot know, He does not exist.
The interesting question (well, to ME, anyway) is, what is it we are CERTAIN that God knows in advance when there exist person's who have the power and the will to change, disturb, rearrange, nullify, invent or corrupt?
I assert that God possessing and using Foreknowledge cannot occur beyond a vague or general "best guess". And that is NOT the same thing as seeing the future in advance.
Scientific Prediction deals with non-living physics accurately enough to --say---shoot a rocket containing a robot off through space and land it in a specific area at a precise location in time and space EVEN THOUGH earth is spinning and so is Mars WHILE revolving about the Sun! That is NOT foreknowledge of the same nature that is attributed to God, however. The Rocket cannot will itself otherwise nor is either Earth or Mars likely to decide to change orbit.
God speakers(people who speak FOR God) fall back on magic as their explanation. That's why it's a dead end. Using magic as the answer for such huge, important parts of your life stops thought, real searching and is intellectually lazy.