Find apache error_log on CentOS

ps aux | egrep '(apache|httpd)' typically will show what apache is running as.

Usually you do not need to change the default user, "nobody" or "apache" are typically fine users. As long as its not "root" ;)

edit: more accurate command for catching apache binaries too

Actually, I probably wouldn't use my other answer in some situations, but I'll keep it there for reference.

If your colleague has been given their own VirtualHost, I would set that virtualhost to output their logs to a different directory, so that they would only see errors for their system:

<VirtualHost *:80>
    ServerName colleagues.vhost.com
    DocumentRoot ...
    ...
    ErrorLog /home/user/errorlog-colleagues.vhost.com
</VirtualHost>

Alternatively, if .htaccess files are enabled, get them to simply output their php error logs to a location they want, e.g.:

/path/to/webroot/.htaccess:

php_value error_log /home/user/phperrorlog-colleagues.vhost.com