Here the term "et al" stands for "and others" and it is followed by (n 35). This means that the total number of others is 35

Similarly in "Charter of the Association of Southeast Asian Nations (n 3)" , here (n 3) stands for number of other nations involved in this charter and it is 3

This is from the 'Overview of International & Regional Human Rights Mechanisms'Seminar.
One of the essential readings for the seminar is;
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Steven Greer and Lewis Graham, ‘Europe’ (Chapter 22) in DanielMoeckli et al, op. cit, pp. 463-480; If you are using the 3rd edition(2018), ‘Europe’ (Chapter 22) pp. 441-459.
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Here 'et al, op.cit 'means 'and elsewhere in the works cited(opere citato(L.) (=그리고 앞에 인용한 책의 한 부분에). * et.al(L.) is the abbreviation for 'et alibi =and elsewhere, & et alii=and others.
Therefore, n 35 might be understood as Chapter number 35. Not the total number or something similar.

English term (edited): n.

It's the abbreviation of 'note', referring to a note above or below the line (with supra or infra).

The note with the number (note 35) in your document will make you see it.

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Note added at 34 days (2023-02-23 16:35:39 GMT)
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But Korean researchers may just use 'n.' in their references. Check Korean academic papers for such references to notes, or ask those who write those things.

Kang Seok Lee’s answer is confused is several ways.
First he conflates “et al” with “op. cit” and proposes the combined meaning to be 'and elsewhere in the works cited.’ “Et al,” however, is separate from “op. cit,” as the former applies to the editor list whereas the latter applies to the partial reference cited from the whole work.
If you look up the table of contents, this book has up to 32 chapters. So it is not a chapter number. rollingup’s answer that it is a note is correct. You will see that between pages 463 and 486, there is a footnote (infra) numbered 35, on page 474.
Hyeonkyeong Lee’s question was about the whole chapter title ‘Europe’ from pages 463 to 486, and what Kang Seok Lee did was to take another, partial citation (only citing up to page 480) from a secondary source, which was a seminar called “Overview of International & Regional Human Rights Mechanisms.”
In “Charter of the Association of Southeast Asian Nations (n 3), article 14,” (n 3) clearly does not mean “ASEAN + 3” as prasanck1 stated. The article does not have notes, which means that the parenthese serve another function in this case.
If you take rollingup’s reference to the Chicago Manual of Style, you can see under the entry [6.94 Parentheses to enclose numbers or letters] that “Parentheses are used to enclose numerals or letters marking divisions in lists that are run in to the text(see 6.123) or to mark certain sublevels in an outline (see 6.126).” In other words, “Charter of the Association of Southeast Asian Nations (n 3), article 14” suggests that the paper to be translated mentions in it the Charter of the Association of Southeast Asian Nations within a list or an outline.