For cPanel server, you can find related logs at /usr/local/cpanel/logs/ folder.
/usr/local/cpanel/logs/access_log
All activity in the cPanel, WHM, and Webmail interfaces.
/usr/local/cpanel/logs/login_log
Logins to cPanel, WHM and Webmail.
/usr/local/cpanel/logs/error_log
Errors that occur in cPanel
/usr/local/apache/domlogs/{DOMAIN}
Domain access log
All other system logs, depends on linux distro that you use, in general can be found at /var/log folder
