A GOOD PRIME LENS
I have the 18-140mm with my D7000 . I was thinking to add the Nikon 50mm f/1.8 g or the 35mm f/1.8g. Which one should I get and why or should I get another lens? We do police work with my German Shepherd and while she is running and jumping I would like a lens that take good pictures of her.
I'm not sure whether you'll like these for what is effectively action shooting. The focal lengths are on the short side and the autofocus is certainly not the fastest in these lenses. But for the money (both are sub-€200 lenses), I can't really suggest a better alternative. The 85mm f1.8 is not exactly a fast focus lens either and it costs more than the other two. But the focus length is much more agreable for the type of shots you have in mind.
For considerably more, you'd be looking at lenses like the Sigma 50-150 and Nikon 70-200 f4. Apart from the fact that the focal length is better, a zoom also means you can better adjust your framing to suit the situation. If you really want the best it is the Nikon 70-200 f2.8. But that lens costs more than 10 times what either of the two primes would cost you.