I'm using Nikon D750 DSLR camera.
How can I capture the rays of light as represented in these two black and white photographs?
I mean in terms of ISO, aperture and shutter speed and filter use.
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The first step is to find a situation where the atmosphere is right for such effects to appear to the naked eye - whether it's steam or fog or dust or whatever else in the air that is reflecting the light. Once you have that, the lens, aperture, shutter and ISO don't matter as much, as long as the combination chosen results in a good exposure and the intended framing. Gear doesn't create the subject matter, it just captures it.
One other thing apart from twalberg's answer is that you need to also be mindful of the focus area, and control the exposure suitably. If you notice in the examples you have posted, the exposure around the light rays are high whereas the start to fall off and darken on the outer edges. This highlights the light ray and makes it pop in the photo.