You can view cPanel access logs, activity, logins and errors for cPanel users and resellers on your cPanel server in the following logs:
tail -f -n 1000 /usr/local/cpanel/logs/access_log – All activity on cPanel, WHM, and Webmail interfaces
tail -f -n 1000 /usr/local/cpanel/logs/login_log – Logins to cPanel, WHM and Webmail
tail -f -n 1000 /usr/local/cpanel/logs/error_log – Errors that occur in cPanel
Please note, root access is required to view these system-wide log files.