How to program SPI interface through SUB-20 device in C#?

Question

C++ / C#

At work, we are starting to program the SPI interface through such a SUB-20 device, I would like to know if someone else is doing this, to find out how the device works. We found drivers and libraries for Visual Studio (C#), but unfortunately there are no descriptions for the function. Essentially I need to know how to read the Slave data register and how to write?