How to view time an employee spent working for each client?

You can configure the Projects Summary report to display the time each employee spent for a particular client. For this:

1. On the Projects Summary report page, check a required employee name in the Team filter and click Apply Filter. 
2. Select a time range you want in the date picker on the right. 
3. Click the Group by button and select the Client category in the drop-down list. 

Note: The report will display only those clients who this user worked for during a specified period of time.