Can an elective class be considered as relevant training required for work?

Absolutely. You're learning the stuff, even if it isn't your major. If the subject is relevant to your job, it doesn't matter if it's an elective or not.

For example, say you major in business or history, but you take a computer class. Maybe you see a job that requires basic knowledge of computers - you can list the class on your resume and on the part of the application that asks if you have any special skills or knowledge.