I don't have a lot of electronic documentation on this since it (the project) is from 2016. Most things are on paper.

This shows a simple way of deciphering the keyboard matrix. This keyboard had 2 separate connectors. One was rows the other columns. Hook them all up to some bread board and start poking around. Depending if your keyboard has diodes built in or not (like this one), you may need to supply a small voltage and currently between pins. I would suggest putting in a series current limiting resistor and LED to better visualize the connection. Quadrille rule paper also helps.