To answer your questions:
What is the passing score for this exam?
- Passing score is 64%
- So you need to get 39 correct answers out of 60, which is almost 2 out of 3 questions.
Which study materials useful for preparation of this exam?
- Magento 2 Certified Professional Developer Study Guide
- SwiftOtter study guide which has explanation to each official study guide questions.
- Magento DevDocs (https://devdocs.magento.com/)
Except from the Free study Guide, are there any other study materials
available for this exam?
- SwiftOtter study guide which has answers/detailed information to each official study guide questions.
Are there any passing criterias for the Commerce (Enterprise) edition just like we have in the Magento 1 Developer Plus Exam?
- M2 Developer Plus certification is not yet launched. It should be launched end of this year.
- M2 Professional Developer does not have any Enterprise/Commerce questions.
What is the retake policy for this exam?
How many free retakes are available?
- No free retakes. In the event that you do not pass the exam, you will receive an email with information on re-testing.
My experience of the M2 Professional Developer exam: http://ka.lpe.sh/2018/08/13/magento-2-certified-professional-developer-exam-experience/