Requirements for part-time jobs at exhibitions vary by position. Some positions require make-up skills, such as make-up artists and models, but not all. For example, booth receptionists, shopping guides and other positions usually only need to have good communication skills and sense of service. Therefore, you don't necessarily need to know how to apply makeup to go part-time at a trade show.
If the position requires makeup skills, you can improve your skills by studying on your own or enrolling in a class.