The "About this material" page can be found in the left-hand corner of the main table of contents:
Note that the button will not appear while on the "Reporting" tab.
The button can also be found in the side table of contents while in a section:
Clicking the "About this material" button will load a modal on the page:
This modal contains information like the class zyBook ISBN, author information, release date, and summary. If your class zyBook is built from more than one catalog zyBook, a tab exists for each catalog zyBook.
Combo zyBooks that contain multiple subjects will contain a drop-down picker to toggle between the info for each subject.