All labels are written out to the
.aux file in lines beginning
\newlabel. The mechanism is described in this answer.
So looking for all instances of
\newlabel in the
.aux file will give you the information you are looking for.
If using the
.aux file for reference, copy it under a new name and use the copy, since the "original" will disappear as soon as the source file is recompiled.
If you are using a *nix system, you can launch (or script) the command
grep \\newlabel *aux | main-labels.txt. This will produce a new file containing only the
\label lines from the
,aux file. This can then be used as a reference.
A comment on the question by @Sveinung provides a similar method for Windows.
Finally, there are two packages that print out the label values on the pages where they are defined in your document:
Both packages report the values of labels that are accessed by
\cite (and friends). Both provide options to include or exclude particular types of labels, and for specifying where to position the reported labels on the output. (See the package documentation for details.)