I would say that Lear achieves wisdom by truly understanding his own predicament and his own self of self in the middle of that awful storm. Prior to that point, Lear had believed that his own wealth had meant value. He believed that with title, property, possessions, and wealth, he was able to externally reflect the sense of respect and dignity that he believed he held and to which he was entitled. When asking his girls to profess their loyalty, he believes Regan and Goneril, primarily because like all else he possesses this is an external representation of his internal hopes. When he walks into the storm and understands that when these external elements are stripped, there has to be a rumination upon what remains and what is internal. When Lear understands this, it is as this point where wisdom, what the Greeks would call "sophia," is present.