Open cPanel → Metrics → Errors to view up to 300 recent web-server error-log entries associated with the account's domains.
The newest entries appear first. Use the timestamps, file paths, requested URLs, and error text to identify whether the problem is caused by a missing file, permission issue, PHP/application error, or web-server rule.
On servers using NGINX as a reverse proxy with Apache, cPanel notes that this interface displays Apache web-traffic errors and does not necessarily expose every NGINX-specific error.