To be able to view your history with a client, your client must have already created an account and accepted your request to access his or her account. You can not view your activity history for clients whose invitation statuses are pending or declined.
To view your activity history with an active client, click on the "History" button next to your client's name. A window will emerge displaying a running vertical timeline of your activity with your client.
However, if you have never signed in to your client's account, you will instead see a "No History: Client does not have any history yet" notification.