take a look at this great blog post http://blogs.splunk.com/2011/01/02/did-i-miss-christmas-2/ where you learn to use the REST endpoint of the
TailingProcessor to show its activities and what files are currently being read.
Hope this helps ...
You could enable debugging on the
TailingProcessor on the forwarder http://docs.splunk.com/Documentation/Splunk/6.3.0/Troubleshooting/Enabledebuglogging and look what is reported in
index=_internal or read the docs here http://docs.splunk.com/Documentation/Splunk/latest/Data/Troubleshoottheinputprocess