How can I tell which questions I have completed?

Within MY RESULTS the progress bar shows you roughly the percentage of work you have completed for any zApp that is not yet due.

To view the actual questions that have been completed you need to open the zApp. Once open the left hand column within the participation window allows you to navigate to a particular question. Greyed out questions have already been submitted.

If you have submitted a zApp you can see the questions you have completed by clicking on the green icon with a tick.