This article shows you how to check your SSL Expiration date in Plesk.
1. Log in to your Plesk Web Admin control panel
2. Search for SSL/TLS Certificate and Click
3. After you click SSL/TLS Certificate, it will enter the SSL/TLS Certificate for domain.com page. Below shows (Valid Until: October 10, 2021) where your Certificate expiration date is.
Another way to verify through Online platforms: https://www.sslshopper.com/