Where do I find the email addresses that the questionnaire survey has been sent to?

To find the email recipient of the notification email, please follow this guide: How-to-Properly-Add-Change-and-Test-a-New-Email-Recipient-Address

If you're referring to the email addresses submitted to your form, you can find it in the Submission Panel. Here's a guide: How-to-View-Form-Submissions

I hope this helps. Let us know if you need further assistance.