Well currently there is not an official channel for Skype for Rasa I don’t believe yet but someone in the community wrote a post about one they made at Skype for Business Channel so maybe you could look at that.
Otherwise you or someone would have to create a custom channel to talk to Rasa, more on that can be found at Custom Connectors which basically uses REST webhook calls to interact with the external channel provider which would be Skype in this case. So you would have to see how Skype’s business API worked.