In the rest of his discourse while trying to answer this question, Job acknowledges that man has perfected the means to search out and mine precious metals and jewels from the earth no matter how deep into the heart of a mountain they may lie. Man digs tunnels through dirt and stone alike to seek out the treasure he desires. Yet there is one treasure that proves elusive. No matter how hard he tries, man is unable to seek it out. It lies beyond our grasp. This treasure is wisdom.
History tells us that the great philosophers of old spent their lives seeking it out wisdom, yet the record of how they lived their lives and of how they died leaves little room for doubt. Whatever knowledge they discovered, wisdom was not found. Job reveals to us that "God understands the way to it and He alone knows where it dwells." Yet God, in His mercy, reveals the path to wisdom to us.
And [God] said to man, "The fear of the LORD-that is wisdom, and to shun evil is understanding." - Job 28:28
The fear of the LORD is the well from which all wisdom springs. If you don't fear God, then you underestimate Him. You don't understand who He is. And nothing could be more important than understanding the nature of your Creator and what He requires of you. Thus, if you do not fear God then you cannot be considered truly wise. You may have attained some measure of earthly knowledge, but wisdom eludes you still.
A person of understanding shuns evil. Anyone who clings to evil actions, thoughts or attitudes is not yet made perfect in understanding. When we embrace evil we bring fire to our chest, for evil surely brings destruction. Our God will not be mocked. We all reap what we sow. Therefore, anyone who willingly pursues evil, destroys their own peace and security. What could be more foolish than this? Only a man without understanding would do such a thing.
Of course, I imagine you are tempted to reject these definitions of wisdom. Likely you do not find them fully satisfying. I Corinthians 1:18-25 shows us that in our sin man always wants to reject God's wisdom, chiefly in Christ but in every other way as well. So if I may push Job's metaphor a little farther, I would say that perhaps this writing hasn't placed jewels of wisdom directly into your hand, but at the least it has revealed a worthwhile shaft to go digging in. Do your own mining of the fear of the Lord and of shunning evil. Here are some other passages that agree with Job's assessment: Psalm 111:10, Proverbs 9:10, Job 1:8, Proverbs 8:13. Find wisdom and understanding in them, and pursue them always.