Send USR1 to the puppet agent process.
kill -USR1 $(cat /var/lib/puppet/run/agent.pid)
and it will reload and run.
Nigel sent you an option to tell the currently running daemon to trigger a new run right now. You can also manually run puppet in a way that will give you more immediate feedback like this:
puppetd -- verbose -- no-daemonize --onetime
This will run another puppet process, which will terminate when the run is over. The original process will do nothing, and continue to run, unchanged by this command.