You can check what all communications have gone out to a specific user till date from the panel or what all activities have been performed by the user till date. For ex : Email sent, email open, email click, SMS delivered, SMS click, any web activity, any app activity, etc.
Below are the steps for checking all the activities against a particular user on the panel :
1) Go to DATA and expand CONTACTS section
2) Select ALL CONTACTS
3) Search for the respective primary key
4) Hover over the contact and click on Details
5) In INTERACTION section, click on TIMELINE