you can listen for this event in the containing page:
you should be able to use that to track using Piwik/Google Analytics etc
if you try different types of download on http://universalviewer.io/examples/ you can see the events being logged in the console
yep! this was added by the Riksarkivet:
if you check the manifest you can see the metadata on each canvas
perhaps you're not using the latest version of the UV? have you tried that manifest by pasting it into the manifest input field here?