As we don't have that particular plug-in to use and test with, the best I can do is give you general information on setting up a vocoder plug-in with Studio One.
If you want to trigger the vocoder from a keyboard, make sure you have a keyboard set as default MIDI device in External Devices.
1. Add an audio track. Place for instance a voice clip on that track.
2. Insert the vocoder to that same track as an insert, vocoder should open. Select a preset.
3. Add a new track. Make this one an Instrument Track.
4. On the Instrument Output drop down of that Instrument Track, select the vocoder plug in. This will route MIDI from your MIDI keyboard to the vocoder track. Select your MIDI keyboard as the input.
5. Press play, you will not hear anything until you play your MIDI keyboard. You could also place MIDI data on this track and it will trigger the vocoder.
If this doesn't help, I suggest starting a thread on the Prosoniq or Studio One forum.