The last notification can be found under "last notification" It shows the most recent client activity, such as completing the search, partially completing it, or just opening the email.
In this example, we can see that the email has been delivered but the client has not yet opened the link or completed the check.
Clicking on the column last notification (so clicking on 'email delivered' here), you'll be brought to the notification page which will give you a breakdown of the activity that has occurred so far.