I'm not sure I understand - does your son have an Xbox 360 at his college location, that he wants to connect to your Serviio server at your home location? If so, unfortunately not possible over DLNA without using VLAN's or the like (which is not for the faint hearted. Requires good/expert networking knowledge and large bandwidth).
Assuming you have
the Pro version of Serviio, your son can however watch movies on his PC, iPad, tablet or phone by using either Mediabrowser or ServiiGo (on Android devices). For Mediabrowser he would connect on
http://ip_address:23424/mediabrowser where ip_address is your external ip address (you can find this at
http://whatismyipaddress.com/).
You will need to ensure port 23424 is forwarded in your router if not already (you can use this to test:
http://www.yougetsignal.com/tools/open-ports/) - the easiest way to forward is to use Serviio to automatically configure your router (on the Remote tab in Serviio Console). If that doesn't work, you will need to search the web on how to manually port forward for your particular router.
Once you have all that going, search Google for "Dynamic DNS" - a DDNS will allow your son to access your home server without knowing your external IP address (which for most people changes from time-to-time, so while OK to test with cannot be used reliably in the longer term).