Note: Not available on all plans. Message support if you are would like email tracking enabled for your account.
Navigate to the contact
Choose the Journal tab
Include "sheep events" in the journal list
A typical view will look like the screenshot below: reading from the bottom up: An entry for the email being sent, an entry for the successful delivery, and an entry for the email being opened.
The problems of spam email and abuse of email tracking have led to the development of email clients that hide the details of email delivery and interaction.