Location of cpanel access logs
General Error and Auditing Logs:
Location : /usr/local/apache/logs/error_log
Description : All exceptions caught by httpd along with standard error output from CGI applications are logged here..
The first place you should look when httpd crashes or you incur errors when accessing website.
Domain Access Logs:
Location : /usr/local/apache/domlogs/domain.com
Description : General access log file for each domain configured with cPanel.
Apache Access Logs:
Location : /usr/local/apache/logs/access_log
Description : Complete web server access log records all requests processed by the server.
MySQL General Information and Errors:
Location : /var/lib/mysql/$(hostname).err
Description : This path could vary, but is generally located in /var/lib/mysql. Could also be located at /var/log/mysqld.log