How do you link within an article to a shared article? I have multisites, article sharing, and the menu component but can't figure out how to simply hyperlink to a shared article from my slave site to an article shared on the master site from within the article itself.

The "Article Sharing for JMS" is the multisites version of the joomla article (com_content component).
It directly read the DB of the other website based on the site ID.

When you create a menu item that use the "Article Sharing for JMS", you have a link that is option=com_multisitescontent....... with site_id="XXXXX" where XXX is the site ID from which the article must be read. The other parameters are identical to the "com_content" component.

Create a menu item with the "article sharing for JMS" to see the parameters that are used by Joomla to access a shared article.