Printer - RBB or CMYK?

I used to know how to do this but it has been so long since I have needed to I have forgotten how. I need to determine if the print pipeline for a certain laser printer is RGB or CMYK. I used to know how to spin up a Photoshop file in a certain way and send to print. IIRC, the procedure was along the lines of make a CMYK document, and create a black square of equal parts of Cyan, Magenta and Yellow. Then slap a smaller 100% black square on top of the CMY square and send to print. Something like that. Does anyone know the correct steps? Thank you.