Commenting no longer working.

To receive an email whenever someone comments on your website, you will have to ensure the following is set in the Dashboard > Settings > Discussion screen:

Email me whenever Anyone posts a comment

This enables emails to your Admin Email whenever a comment is posted.

If that option is set on your install, and you still do not receive emails when a comment is posted, then there are a number of issues that can cause this.

For example, the server could be blocking outgoing emails.
Or, in your Settings > General > Administration Email Address perhaps a wrong email address is added.
Or, your mail inbox is moving the emails to the spam or else folder.

To check if the emails are sent, you could install a plugin like https://www.ads-software.com/plugins/wp-mail-log/. This plugin will log all emails sent by the website, so you could narrow down the issue (if the plugin logs emails as successfully sent then you would know the receiving end, your mail inbox, is doing “something wrong”)
On the other hand perhaps that plugin log will show an error such as “email could not be sent because of … error”
That would tell more about the error, and from there you could take accordingly actions to fix that.

I hope this helps for a start!