Can I Publish a Book Based on my Ph.D. Thesis and Other Practical Findings I Found After My Ph.D? I have a followup question after getting the answer on the following question: Who Owns the Publishing Rights of my Ph.D. Thesis?. 

After my Ph.D. I did work both in industry and in academic, and I think I have a reference book in me based on the theory side of my Ph.D. thesis and the practical knowledge I gained developed those theories (using main stream programming languages in my case); and the teaching experience on that matter.  

So, is it possible to write a reference book based on theory contributions of my Ph.D. and practical findings based on those theories?
There's several issues here.  One is the copyright of existing work, for instance your thesis, work you did for a company that now belongs to them, papers published in journals where you assigned the copyright.  That covers the specific words, figures, code and data you used in those places.  You may or may not have rights to those, depending on the terms of the agreements you made.

Another is confidentiality, for example obligations to your employer, trade secrets, upcoming patent applications, state secrets, etc.  You don't want to reveal things you aren't allowed to reveal, by either contractual obligations or law.
Law may also cover libel, hate-speech and other restrictions on freedom of speech.

Beside that, what's in your head belongs to you.  So if you sit down with an empty piece of paper and just write, all that belongs to you.  And if you want to publish that, nobody can stop you.