On web:

In the Questionnaires tab, you can see your past questionnaires, these are already fully completed.
Here you will also see your pending questionnaires and their progress.

 

In the app:

After having filled out the questionnaire, you can see on the list of Tasks, that your questionnaire is completed.

If the questionnaire isn't completed yet you will be able to re-open it in the "Tasks" section. You can also see the progress of your questionnaire.

If you want to view this several days after filling out the questionnaire, please go to "Timeline", here you can see when you've completed the questionnaire.