CDL Licence

Hello. I'm an ex owner operator that sold my truck 20 years ago. I'm thinking about driving a company truck, after turning wrenches since. I have a Class A with PX endorsements, but no L endorsement. I have 2 questions. Is the air brake endorsement covered with the PX endorsement, or do I have to get one added? And, do I have to start over with a cdl school, or can I get a refresher course and get hired by a company? Thank you