The below books are a recommended reading list that I think will help in the development of your goalkeeper
Which ones should I read?
All of them eventually
Which one do I start with?
Doesn't matter just start. It's the start that stops most people.
How often should I read?
I recommended minimum 10-15 minutes every day. Before bed in a nighttime routine is what we recommend.
Below are books from Sport Psychology, Leadership, and Developing Talent
Reading sport psychology is a way to intentionally train that aspect of the game.
Leadership is a skill that needs to be developed. Gaining knowledge from these different books will give your goalkeeper ideas and strategies they can start to develop.
Developing Talent books give your goalkeeper ideas into motivation, habits and studying success. The more you value something the more motivated you are to do it. I believe that learning about these things the goalkeeper will value what they are doing more and in turn be more motivated to do them.