Adobe Reader can export and view a list of comments through the Comment tab on the right side.
In Evince PDF viewer, the side pane has a drop-down annotations menu that lists comments.
F9 key if you don't see the left-hand panel.
I have also read that you can extract all comments and annotations from a PDF file by
apt install texlive-latex-extra pdfannotextractor --install pdfannotextractor in.pdf
This yields a
.pax file without plain text.
However, it was not clear how to read this file.