'Knows' in the Bible

And who knows whether he will be a wise man or a fool? Yet he will have control over all the fruit of my labor for which I have labored by acting wisely under the sun. This too is vanity (futility, self-conceit).

Who knows if the spirit of man ascends upward and the spirit of the animal descends downward to the earth?

A poor yet wise youth is better than an old and foolish king who no longer knows how to receive instruction and counsel (friendly reproof, warning)—

For who [limited by human wisdom] knows what is good for man during his lifetime, during the few days of his futile life? He spends them like a shadow [staying busy, but achieving nothing of lasting value]. For who can tell a man what will happen after him [to his work, his treasure, his plans] under the sun [after his life is over]?

for you also know that you too have cursed others many times.

Who is like the wise man?And who knows the interpretation of a matter?A man’s wisdom illumines his face,And causes his stern face to beam.

and I saw all the work of God, I concluded that man cannot discover the work that is done under the sun. Even though man may labor in seeking, he will not discover; and [more than that], though a wise man thinks and claims he knows, he will not be able to find it out.

For I have taken all this to heart, exploring and examining it all, how the righteous (those in right standing with God) and the wise and their deeds are in the hands of God. No man knows whether it will be love or hatred; anything awaits him.

For man also does not know his time [of death]; like fish caught in a treacherous net, and birds caught in the snare, so the sons of men are ensnared in an evil time when a dark cloud suddenly falls on them.