Ohh.. that looks cool. I don't have a lot of experience with MIDI controllers yet but I do have a Numark DJ MIDI turntable thing. Sometimes I use the faders on it to record automation on a track or two in Reaper.
If you're using Jack and Carla (or similar) here's what I'd do.
Open Carla or QjackCtl or something so you can see what changes on the graph when you plug it in.
For me when I plug in a new device it add a new midi_capture in the "system" list. Connect that to one of Reaper's MIDI inputs. In my example I'm connecting "midi_capture_2" to "MIDI input 2"
Then in Reaper I open the preferences (ctrl+p) then go to Audio > MIDI Devices. In the top list I set the mode for midi_capture_2 to "Enabled+Control".
Now as a test I create a new track with the plugin "ReaControlMIDI". Towards the top-right of the plugin is a button, "Show Log". Click that and then move stuff on your controller. If you see data then all you have to do is map your controls.
This is where things get tricky and I won't be able to help too much since I'm still learning the ropes myself.
ReaLearn seems to be the best way to configure random MIDI devices to do whatever you want.
https://www.helgoboss.org/projects/realearn/#getting-started
If you have ReaPack
- add the repo - https://github.com/helgoboss/reaper-packages/raw/master/index.xml
- search for "realearn" and install
Update: I decided to spend some time learning more about ReaLearn and found that there are already some mappings for the NanoKontrol2. I've also seen a few different sources say you need to use the Korg Kontrol Editor software to make a few config changes on the device. I don't have the device but I did test the software in WINE and it at least installs and opens. I've had to do this with Behringer software before and it works fine.
https://github.com/helgoboss/realearn/blob/master/doc/controllers.adoc#319-korg-nanokontrol2