Trebek’s final episode of “Jeopardy!” is set to air Friday, Brad Rutter — one of the highest-earning contestants on the trivia series — fondly recalls a time when the veteran trivia emcee hilariously opened the show in his undies. Rutter, who racked up a cool $4.6 million as recurring “Jeopardy!” contestant, remembered the seemingly straight-laced Trebek flexing his funny bones during the show’s 2005 “Ultimate Tournament of Champions.”“We were so nervous, we were just all pale as a ghost,”