I was not able to locate a suitable cmdlet in the PSTK (or an API call, actually) after looking quickly. If your environment allows for SSH, you could use the Invoke-NcSsh command like so (after connecting to a controller, of course):
Invoke-NcSsh -Command "network connections active show"
thanks for your answer. What is the best way to filter the whole thing afterwards? If I see it right I will get a long string with all active network connections. I haven't found the right approach to use the data yet.