Nikkor AF-S 50mm f1.4g any good?

Is that lens any good with Nikon D7200? What would be the focal length, if it's DX?

Yes it's very good.

It's focal length is 50mm. It doesn't magically change according to what camera you mount it on.

It's field of view would be equivalent to a 75mm lens on a 35mm (full frame) camera, but unless you also have one of those and use your lenses interchangeably between them, it's irrelevant.

Is it good with the D7200? Only if you know how to use it. The 50mm is a good lens for portraits and for shooting in relatively low light conditions. It's not good for landscapes and distant shots. It can be used for action though at near distances.

What focal length would it be? Silly you. It's 50mm of course! Focal length does NOT change from crop to full. Only angle/field of view does. On a DX camera, the 50mm lens will see like a 75mm lens on an FX camera.