Real systems require real info. If he doesn't want to pay for the info he shouldn't be working on the systems.
These systems are complicated enough that all the available info is a minimum for analysis. You should know that anyone working on these systems for the first time is bound to cost someone lots of money in training.
The "Introduction to Service" is an overview of the technical theory of new systems and will be a good start for learning. Some repairs can be started from the book. Unfortunately its not the whole story. It doesn't have complete wiring diagrams and it doesn't list diagnostic procedures.
I would suggest that you limit your use of this tech to service items and parts replacement. His lack of interest in his trade can't work to your benefit.
Bosch Master, ASE Master, L1
33 years MB technician