When you are looking at your publication, you use the Share menu, and you'll see this dialog:
As it suggests, copy the URL to the Clipboard. Then click on the Facebook (or other) icon.
You'll then be taken to this Facebook page in your web browser:
Use the menu to specify how you'd like to share the URL.
Thanks, Steve Werner.
It was an unfinished document that I posted from my iPhone, and couldn't find a ready path.
Appreciate the feedback.
Thanks to Steve Werner.