When Jake walked into the jewelry store the salesperson is reading off a list of purchases to the old man. She says "one watch, engraved to Carolyn. Happy graduation counselor." Jake overhears this and is able to extrapolate that the watch is for Carolyn, and that she has just graduated from law school (you call lawyers counselor). The salesperson then says the old mans name (Tom Lewis) when telling him she'll be right back. Jake now has all of the information he needs to trick to old man into thinking he is a law school friend of his daughter Carolyn. The fact he assumes that Carolyn was the old mans daughter was a shot in the dark that he had to take. That is why the character of Jake Vig is a good con-man.