Where are you looking for it? The input should be midi and so add a midi track. Once you have done that, in the mixer window look at the track you just added and click on the input selector. (see http://manual.ardour.org/ardours-interface/audio-midi-mixer-strips/ ) you should see your keyboard listed there.
Oh my, I can’t see any reason to use jack on windows at least not for this reason. You are reading something that is probably quite old. Jack has not been required to run Ardour for some time now on any OS.
The big thing to remember here is that you are dealing with MIDI not audio. therefore it will not show up as an audio device. Feel free to select your system audio device for audio. Ardour does not select one MIDI device or the other but sees all of them and each midi track can select which of these devices to use.