We really like the book series called ‘The Missing Manual’, they provide easy-to-understand helpful information. They are also great reference books if you have an occasional how-to question. If you are a LaLa client looking for a deeper understanding of WordPress. The WordPress: The Missing Manual may be a good fit for you.
The second edition only covers up the WP 3.9. They have released the third edition. We hope it covers WP 5.0 and the Gutenberg Editor, but haven’t had the opprtunity to read the new edition yet. Other than the Gutenberg Editor the WordPress core functionality has stayed the same, so the second edition is still chock full of useful information.