View attendees of a meeting which I already accepted in Outlook 2016

Peter, you can just open the event, and click the Scheduling Assistant button in your second screenshot to view other attendees:

If you have Outlook Social Connector, you can see meeting attendees via the People Pane:

To open the People Pane, click on "View > People Pane", and then "Normal" inside the main Outlook window.

You can also click "Respond" then "Reply To All". Outlook will create an email populated with the participants. You can then discard the draft. (Office 365)