Q. How should one cite a published book that is in an archival (personal papers) collection? The most important element of the book is not the text but the annotations added by the person whose collection the book is in. Thanks!
A. Cite the book like any other book; then cite the archive according to the advice and examples in CMOS 14.119–29, prefacing this information with “in” if it immediately follows the book citation (cf. CMOS 13.25).
The goal is to make it clear which book you’re citing and where the copy that has the annotations can be found. The annotations themselves can be discussed anywhere—in your text, in your notes, or in an addendum to a bibliography entry for the book (see CMOS 13.68, item 3)—and you can cite specific page numbers where applicable. But the annotations wouldn’t be cited as a separate entity.