Using PowerShell, you can search Active Directory for the Password-not-required attribute and see which accounts on which this may be configured. Another approach is using this free tool that provides an automated way to gain visibility to not only blank passwords, but also many other dangerous passwords such as breached passwords.
With a quick scan, you will be presented an overview containing various password vulnerabilities in your Active Directory. The individual reports can be accessed by clicking on them to reveal additional, more detailed information. Click here to learn more.