Then it still matters a lot what kind of codebase he is working on. A web project is differently structured and done than the codebase for a embedded operating system. There are differend standards and practices in the industry.

I learned a lot by just stepping through the code with the debugger of libaries I used. That brought more practical insight while learning about design patterns etc. In the end, it is all about patterns. Finding the right pattern for a given problem.