Connect these verses with Ecclesiastes 6:2-3 : “All labor is undertaken with a view to some profit, but as a rule the people who labor are never satisfied. What advantage then has he who labors if (being rich) he is wise, or if being poor he knows how to conduct himself properly; what advantage have such laborers above a fool? (None, so far as they are without contentment, for) a thing present before the eyes is preferable to a future which exists only in the desire.”
What - literally, what profit (as in Ecclesiastes 1:3).
Knoweth ... living - i. e., “Knows how to conduct himself rightly among his contemporaries.”