The Chicago Auto Show management does not hire individuals. Rather, it retains firms that provide ushers and security. For such work, contact AF Services, (630) 279-0500. Many other workers in the building are employees of McCormick Place, (312) 791-7000.
People who set up and dismantle the displays are arranged for by the show's general contractor, GES Exposition Services, (773) 767-2237 or email@example.com.
As for the people who work in the various exhibits, they are hired by the vehicle manufacturers, like Ford, Chevrolet, and Dodge. For those opportunities, suggest you turn to the websites of the vehicle manufacturers and search the sites either for Employment or Contact Us.