The already mentioned The Pragmatic Programmer, 20th Anniversary Edition is so far the best I have read. It's not overly specific to one single thing, it tries to teaches general principles and good practice.[1]

I also have a personal recommendation for when you want to better understand testing, QA, or want to/have to work with QA people. [2]

[1] https://pragprog.com/titles/tpp20/the-pragmatic-programmer-2... [2] https://www.amazon.com/Lessons-Learned-Software-Testing-Cont...

Point him to "Lessons Learned in Software Testing" by Bach, Kaner and Pettichord: http://www.amazon.com/dp/0471081124

Also, "manual testing" is a slightly unfortunate monicker for the activity we are discussing. It is bound to generate some degree of incomprehension or even hostility on the part of some people, for no foreseeable benefit. "Testing" will do. It is something you do with your head primarily, your hands being involved to pretty much the same degree that they are in programming (and we don't usually call that "manual programming").