By default, debug messages aren’t logged. If you have a problem with WordPress and need to see the error messages, you’ll need to turn on WordPress’s debug mode. This will create a log in the wp-content/ folder of your WordPress install. The file is called “debug.log”.
You have to add a line of code in your wp-config.php file to enable this. This is very easy to do from the CPanel if your host provides this as many do.
Before starting, please make a backup as if you accidentally miss a colon you’ll get up with a broken website. You want to be able to quickly roll back if you run into trouble.
I would also advise doing this on a duplicate of your live site ( staging site ) so that your live site remains unaffected. An exact duplicate of the site should show the same errors as the original.