Most personal training textbooks are available through the internet. If you go to www.amazon.com and search for ‘personal training’, you should get quite a selection to choose from.
Personal training books can be pricey but it will be worth it to look for the best. Anything promoted by ACE, NSCA, NASM, or ACSM(national certifying organizations for trainers) should be fine. What kind of training would you prefer to do or learn about? There is strength training, sports training, weight management, older adult and youth training, etc.