Citation, Documentation of Sources

Q. Perhaps the most important quote for the paper I am writing comes from the footnote of something someone wrote in a scholarly journal. Is there a particular way I should have to endnote this since the quote comes from a footnote?

A. Yes. In addition to the page number, give the note number: 256n4.

[This answer relies on the 17th edition of CMOS (2017) unless otherwise noted.]