Maske <maske1foro@gmail.com> writes:

The headings could be in different files, yes.

AFAIK, citations don't link two exact points. Footnotes do.

Do you mean that you also want to jump back-and-forth between footnote
definition in the another file and its footnote references?

Right: With C-c.

And maybe there could work directly commands like "org-footnote-action", being unneeded to create new commands like "org-note-action" with almost the same functionality.

I don't understand the option of "include", but I think it wouldn't be 
the case.

See https://orgmode.org/manual/Include-Files.html

I really think footnotes would be a particular case of this option.

** Reference in file A
:PROPERTIES:
:ID:       978-84-362-7195-9
:END:

...
A “comment line” starts with a hash character (#)
*[n:102@978-84-362-7195-9]* and either a whitespace character or the
immediate end of the line.
...


** Notes in file B

*[n:102@978-84-362-7195-9]* The hash character is important in orgmode.

May you explain the purpose of @978-84-... part?
You seem to assume that a footnote always has a single reference,
which may or may not be the case in practice.

If there would be more than one reference, a behavior like that of footnotes would be appropriate?

The purpose of the @978-84-... part:
@978-84-362-7195-9 would work like the ID for internal links: [[id:978-84-362-7195-9]]. That would allow jumping to the correct heading from any file. 
I am not a programmer, so the syntax I am sure could be more solid.  Example:


** Reference in file A
:PROPERTIES:
:ID:       978-84-362-7195-9
:END:
...
A “comment line” starts with a hash character (#) [n:102@978-84-362-7195-9] and either a whitespace character or the immediate end of the line.
...


** Notes in file B
[[id:978-84-362-7195-9]]: Link to heading in file A

[n:102@978-84-362-7195-9]: Link to an exact point in file A. Where the point is defined by the LABEL 102, and the file can be find thanks to the ID 978-84-362-7195-9