cPanel or WHM Accounting Logs:

Location : /var/cpanel/accounting.log

Description : Contains a list of accounting functions performed through WHM, including account removal and creation..

cPanel error logs:
Location : /usr/local/cpanel/logs/error_log
Description : cPanel logs any error it incurs here. This should be checked when you encounter errors or strange behavior in cPanel/WHM...

Client Information, Requested URL Logs:
Location : /usr/local/cpanel/logs/access_log
Description : General information related to access cPanel requests is logged here.

Bandwidth Logs:
Location : /var/cpanel/bandwidth
Description : Files contain a list of the bandwidth history for each account. Each named after their respective user.

Apache Access Logs:
Location : /usr/local/apache/logs/access_log
Description : Complete web server access log records all requests processed by the server.

Message Reception and Delivery:
Location : /var/log/exim_mainlog or /var/log/exim/mainlog
Description : Receives an entry every time a message is received or delivered.

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