Login to your Postmark account and from the main dashboard, click on your server name:
Then click on "Default Transactional Stream":
From the "Statistics" screen, you can see metrics for all of your transactional email sends, and you can filter it down to the campaign level by click the dropdown that says "All Tags". You create these tags when you setup the Transactional send action in the automation.
You can click "Activity" to bring up a table that lists all transactional email activity. You can use this to search if a specific contact is opening or clicking your emails.