Here is a blueprint for the dan k'ni form the last youtube video!
That one : https://youtu.be/ddSc2ijJCBg
This instrument is inspired by the vienamese dan k'ni
https://www.youtube.com/watch?v=f9WVTb83KUM&ab_channel=thedannvhn
https://www.youtube.com/watch?v=IN7jqLGkrcs&ab_channel=MattLaufenberg
The shape of the instrument is very simple, I have to work on some new prototypes, this one is very simple but it works,

The tricky part is the sound transmission, I used a standard hemp rope, it also works with cotton rope, there is a knot on the bowed string, and some glue to fix the rope on the string (if you don't it will slip).

The mouthpiece is a piece of plastic box lid, with a hole in the middle and a simple knot on the rope. The size has to be confortable in your mouth (it's not), holding it with your teeth.
I made an instrument with frets, easier to play for me, but you can make a fretless instrument if you prefer, You can use any online calculator to know the emplacements of the frets, like this one https://tlcguitargoods.com/en/howto-fret-calculator.
I don't know the traditional way to make a fretboard, so I used bicycle spokes with glue.

On this one I put an electric guitar string (A-5), a quite low version, I also have a second instrument I made with a higher string (B-2), closer to the original instrument,
I didn't try with a violin or a cello string, tell me if you do!
Tell me if you have questions, or if you make your own prototypes, I'll update this article!