Exr-IO (free plugin to import EXRs) extracts the metadata and displays it in Photoshop "File Info..." -> "Raw Data". You can find the passes here as well:
<rdf:value rdf:parseType="Resource">
<exrio:name>corona.stats.passes</exrio:name>
<exrio:type>int</exrio:type>
<exrio:value>63</exrio:value>
</rdf:value>
I would love to find a command line tool to view all metadata without the need of opening the entire file in any application. But maybe there is even a python module capable of doing it, no time to test/search so far.
Good Luck