It depends a lot on the person and how they prefer to learn.
For people who are very analytical and self-motivated, i think it's fine to suggest reading books fairly early on in their development and just be there to answer questions or indicate how those theories are applied in the company's processes and tooling.
In this case the challenge is more around finding a book to suggest that suits the work. Coaching can end up being more around where to focus or how to skill up on one topic at a time.
Some people find it tough to digest knowledge in written form. In my workplaces this is often compounded by many good tech resources only being available in English and many developers not being native English speakers.
In these cases i have found it helps to start with pair programming (best case) or detailed code review (at minimum). After each "learning session" you can then provide links to references (book, article etc) for more info or background on the comments. This helps contextualize the theory upfront and shows the value of the source.
Sometimes when a certain source is referenced frequently, people take the initiative to read it to better understand the fundamentals for future work. Sometimes they don't.
That's where management comes in, i think. Regardless of whether a person chooses to learn with a book or some other source, at some point they are going to have to be able to solve challenging problems on their own. Managers are able to facilitate growth by allocating tasks that are at the right level of complexity for the dev.
I think the point is that it's not the job of a mentor to step in and solve the mentee's task, but to provide support and explain what sort of techniques and resources may be helpful to solve it. It's still up to the mentee to do the work.
Thank you for the detailed answer. I know this is somewhere I still have a long way I could improve so it's definitely interesting to get another's thoughts.
