Are you using Linux? If so, as others mentioned, you access the data using wireshark/tcpdump, filtered for the IP, while using that software.
On the server, you can try running netstat or a similar program depending on your OS that will tell you what ports are being listened to. Use the man page to see if further options (such as what the program command line is for each listened port) can help you narrow it down.
Or you can drop the firewall temporarily and run NMap against the server, scanning all ports, to see what's open. Or scan it from behind your firewall if you're not running a software firewall. Note the open ports and investigate.
If it is on Linux (or some Windows machines) you can look in the config files to see if they have a port specified.
Last, see if you can get in touch with any of the ex-developers from that company, or other customers of that software and see if they can help; if you can find any of them, maybe they know of other customers or have a support forum or other admins that are running the software that can get into a mailing list to help each other out.