From the docs:
Depending on how you enable RUM, monitoring data is sent to Dynatrace within varying request types:
when you are considering RUM for mobile (as you made in your tags), that for SaaS data are sent on 443 port directly over internet. On Managed it's not as simple. In most cases Dynatrace Managed cluster cannot be reached from internet. In such cases when you don't have instrumented WebServer that serves API, you can use Cluster ActiveGate which has default public port (SSL) 9999 for external communication (can be changed). If you have instrumented by OneAgent web server that servers API for application, you can configure DT to listen on this API uri on 443 port (DT is adding extra rb_XXXXX endpoints that consumes data from RUM). To make it work like that you have to go to your application settings in dynatrace and change default behavior which is using ActiveGate (or exposed cluster).
Just to make the complete answer - regarding the traffic - you can see in CMC what's the traffic processed by Cluster AG. But that's not only RUM traffic. To have some better measurements you'll need to check it in self-monitoring if you have access or ask Dynatrace team to provide that data.