How often do we say the phrase "who knows?" in response to some question? This is a funny thing to say, since there is Someone that knows right? Most likely there are at least 2 that know. There is at least one person that is likely to know, and then there is God. Even other belief systems besides Christianity regard God as an all-knowing type of entity. The Bible supports His omniscience.
I've often caught myself saying "who knows" and subsequently hearing a little voice in the back of my mind say "God does."
"Nothing in all creation is hidden from God's sight. Everything is uncovered and laid bare before the eyes of him to whom we must give account" Hebrews 4:13