The exam's official web page is https://www.microsoft.com/en-us/learning/exam-ms-101.aspx. I always recommend checking the exam information page to make sure you're preparing for the latest skills included. Things in the Microsoft world change quickly, and new concepts may be added at any time.
The exam page allows you to schedule your exam (to take it remotely at your home or at a certified test center) and review the skills measured in the exam. Currently, it lists the following:
- Implement modern device services (30-35%)
- Implement Microsoft 365 security and threat management (30-35%)
- Manage Microsoft 365 governance and compliance (35-40%)
You'll notice these match the three parts to this book outlined in the Table of Contents. Within each of the three parts, the book is broken into chapters in which you'll find the specific skills measured and their associated subtopics.