Given that the "Opened and downloaded documents, viewed items in lists, or viewed item properties" audit event is unavailable in SP2013 Online, what other options are there for tracking who is opening or downloading what? Why is this even disabled in SP Online?
Source: https://support.office.com/en-za/article/View-audit-log-reports-b37c5869-1b47-4a82-a30d-ea20070fe527