How can I create a compound query (filter) that searches both Epics and Stories (via a join) and then shows multiple (and some duplicate) attributes (e.g. "Summary") for both the Epics and Stories in a single listing.
JQL is for finding issues, it has nothing to say about what to display about them.
So, the first part of your question is easy - issuetype in (Epic, Story)
The second part about displaying them simply goes back to what you are displaying the filter in. If it's the issue navigator, you can tell it to show you the summaries and sort by them for example.
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