Well you could use the tmadmin subcommand printservice to see if there have been any requests processed by the service. That would be one way. Another is obviously to have some test client that actually invokes the service. If the service uses FML or FML32 buffers, you could use the ud or ud32 commands to create a request to send to the service.
If you check the Tuxedo documentation, it has a section on monitoring Tuxedo applications with tmadmin. Alternatively if you need to do more detailed or complex monitoring, there is an add-on product called TSAM (Tuxedo System and Application Monitor) that can provide detailed monitoring information about a Tuxedo application.
Oracle Tuxedo Chief Architect