CB radios are used by hundreds of people, from ham radio operators to semi truck drivers, for communication and even entertainment. If you want to learn how to repair a CB radio then your best bet is to find some official training to help you get on the right track. Once you've learned the basics for electronics and radio repair, you can then enhance your understanding through further courses, reading materials and Internet discussion on the subject.
Check your local options for education. Technical colleges offer certificates in radio repair and associate degrees in the more general field of electronics repair. Earning the appropriate degree so that you can gain a firm basis for understanding radios and how they work is a good first step.
Read books on CB radio construction, repair and troubleshooting. Once you understand the basics about how these radios work and the components they're made out of, you can then follow up by going in your own direction. Whether the books you read are textbooks or just the do-it-yourself manuals you can find in any bookstore, the more you know, the better your knowledge base for CB radio repair will be.
Converse with other CB radio enthusiasts. The Internet is filled with forums and websites dedicated to CB radios, their building and their repair. If you can read through these areas and communicate with other enthusiasts, you can exchange knowledge and grow your own base even larger.