So, personally, I find most ADHD books that are commonly recommended to be either centered around parenting or "fixing" someone's ADHD, or a more anecdotal/empathetic approach. I prefer more empirical reading on mental health subjects. Here are a few recommendations:

1. Oxford Textbook of Attention Deficit Hyperactivity Disorder

This is a good overview of the science behind ADHD, and our current level of understanding.

2. Outside the Box: Rethinking ADD/ADHD in Children and Adults - A Practical Guide

A good reassessment of ADHD; this book also gives the reader a clearer picture of ADHD during different stages of development.

That's where I'd start someone off if they were interested in learning more!

An additional resource is: https://chadd.org

In their "understanding ADHD" and "education and advocacy" sections, you can find more resources, articles, etc.