Where can I view the reminder invoices I sent to a client?

Hello, vkarnofski. 

I'll show you how you can view the sent reminder invoices in QuickBooks. 

You can use the Audit log to prove that the reminder email has been sent. Simply go to the Gear icon, then select Audit log. 

Set the Date changed drop-down menu to when the reminders were emailed. Check the "Emailed" detail under EVENT.

Take note that the report will only show that the invoices were emailed. It won't specify details if it was a reminder email however. 

If you'd like to learn more about the Audit log, you can check this article: Use the audit log in QuickBooks Online. 

Do you have any invoices that were left unpaid and you can't collect the payments anymore? You can write them off as bad debts. Check this article if you need a guide: Write off bad debt in QuickBooks Online.

If you'd like to know more about handling invoices or any transactions in QuickBooks, please don't hesitate to leave a reply. I'll get back to you with the details and help you out.