Logs for the following cPanel services can be found in the following locations.
These log locations will require ‘root’ (administrator access), if you do not have this, please contact your hosting provider

Access Log for cPanel, WHM, Webmail

usr/local/cpanel/logs/access_log 

Error logs for cPanel Pages

usr/local/cpanel/logs/error_log 

Login Authentication into cPanel

/usr/local/cpanel/logs/login_log 

ModSec Audit Log

/var/log/apache2/modsec_audit.log 

Email’s processed through server

/var/log/exim_mainlog

Email IMAP/POP3 Authentication

/var/log/mainlog

FTP authentication and errors

/var/log/messages

SSH

/var/log/secure

Apache HTTP Web Server Log

/usr/local/apache/error_log

Individual Site Logs (Separated by domain)

/usr/local/apache/domlogs/[domain]
/usr/local/apache/domlogs/[domain]-ssl_log 

If you do not have access to root, these logs are also located within the users cPanel account

/home/[~username]/logs/[domain]-[mmm]-[yyyy].gz
/home/[~username]/logs/[domain]-ssl_log-[mmm]-[yyyy].gz