An easily answered question, but in 1950, producer Mark Goodson answered the question most eloquently with a pioneering panel show called "What's My Line?". For seventeen years, and another seven in syndication, a parade of people with the widest variety of jobs you could imagine passed by a panel of four whose job it was to ask questions to find out what they did. "No" responses caused the questioner to lose his or her turn; ten "No"'s and the contestant won $50.
In 1975, ABC (of all networks, since "WML" remained CBS property) mounted a 25th anniversary special for the show, featuring Mark Goodson, panelist Arlene Francis, and original host John Daly. Thanks to the good offices of Mike Klauss, you can see this special. Part 1 is embedded below, and you can easily get to the other eight parts from there. Enjoy.
On the same subject, J. Keith van Straaten is currently mounting his What's My Line Live Onstage show in New York City on Monday evenings - check it out!