Not knowing how familiar you are with cameras of this size so the clipped corners of the ground glass are to let air out of the bellows as the camera is closed and by looking at the aperture through the clipped corner you can determine if the selected aperture will vignette or not. If you can see the aperture edges it will not vignette. This is true if the lens covers the format.
I had a Sinar that used a fresnel on the back side of the ground glass. It was as easy to focus as a Graphic with the fresnel in front of the ground glass.
Get one of these and experiment before committing to a more expensive photo dedicated fresnel.
https://www.officedepot.com/a/products/671085/Sparco-Handheld-Fresnel-Lens-Magnifier/
Cut it to fit the gg opening with clipped corners. The ribbed side goes against the gg.