CCAI is Cisco Certified Academy Instructor. First, you have to be associated with a Cisco Networking Academy. Second, you have to go through appropriate training in the course you want to teach for the CNAP. Most instructors are in the CCNA program. For CCNA instructors, you have to go through the four semesters of curriculum as a student with training from a Regional Academy instructor. This is often done with four separate one-week classes for each of the curriculum semesters. To complete the classes you have to take online exams and pass as well as hands-on skills exams for each semester. You also have to develop lesson plans and demonstrate teaching ability during the training. After that, you will be provisionally certified to teach the material but you still have to pass your CCNA exam. After you complete the CCNA exam you will be CCAI-CCNA. If you already have your CCNA, there is a fast-track program you can enter to get the CCAI-CCNA. That is a one-week program where you take the hands-on skills exams and demonstrate teaching competency. Very few instructors do the fast-track. If you want to teach other courses under the CNAP, you have to train and certify in those separately.
Those are the high points.
HTH