I’m using Scrivener 3.0 for Mac for the first time in a while (I used to use 2.0).
Previously, I used project notes in Inspector. I can access the notes are for indivdiual files and folders.
How can I access notes in Inspector for the entire document?
Appendix E, What’s New, in the user manual PDF, is a good place to go when looking for tips on how to find features that have changed or moved in Scrivener 3. E.5 covers Project Bookmarks, which are a collection of features that replace the Project Notes feature from 2.x.
§10.3, Project and Document Bookmarks, pg. 234, is where Bookmarks in general are discussed. Skip down to §10.3.2 for notes on how to access bookmarked items in the Inspector, like you used to do with Project Notes.
Lastly, here is a blog post on Project Notes / Bookmarks.