I am currently writing a non-fiction book which I intend to self publish. Regarding the citations and references, I intend to list them at the end of the book as endnotes and have decided to organise them by chapter which means the numbering will reset every chapter. E.g. Chapter 1: 1, 2, 3; Chapter 2: 1, 2, 3, etc.
So, what if I cite the same source multiple times across different chapters? Do I have to continue to cite them again in my endnotes under each chapter?
If you treat your chapters as separate entities, then: it is expected to restart the count for the citations for every chapter, and to cite again material regardless of whether it was already cited in other chapters.
If your chapters are not separate entities, then there is no benefit in restarting the citations count, and you can just restate the number of the cited source every time you mention it.
If you are stuck on your setup, then for each source that was already cited in Chapter X as [n], you can cite it in Chapter Y, and in the end notes just write the reference as:
Chapter Y, ref m: see Chapter X, ref n.
One common method is to have a "list of works cited" with full bibliographic information for each, and a unique abbreviation for each. Then notes list only the abbreviation and the page number. This is particularly useful when many of the works are cited multiple times.
Some authors, after citing a work once, will cite it the next few times abbreviated as "Ibid., xx." See https://libguides.up.edu/chicago/short_form
