John F. Kennedy Jr. is a prosecutor-in-the-making. Kennedy, 28, a third-year law student at New York University and son of the late President John F. Kennedy, will join the Manhattan district attorney's office in August in a $29,000-a-year job. Kennedy won't have time to pass the bar exam before starting the job so instead of making courtroom arguments, he will start his career by doing research and leg work. The new job brings up a couple of interesting bits of trivia: Kennedy's boss-to-be, District Attorney Robert Morgenthau, was appointed to a U.S. attorney's job by President Kennedy in 1961. Also, the job young Kennedy is taking has been a stepping stone for the sons of Dan Rather, Mario Cuomo and Cyrus Vance.