Which Nikon lens to use to achieve this type of photo?

The 35mm F1.8 or 50mm F1.8 would be great go-to options:

https://www.bhphotov...0mm_f_1_8G.html

I'd probably go with the 50mm, since the longer focal length lets you get shallower bokeh.

I don't see any photos attached, but I might go even longer than Adam suggested if you want very narrow depth of field (a small slice of the image that is in focus)--perhaps consider an 85mm f/1.8. Adam's suggestions are a bit more affordable than the 85mm, but the 85mm f/1.8 isn't terribly expensive. But definitely the 50 over the 35 if you need to stay low budget.

I don't see an attached image either so it is hard to determine the range you are hoping for.  Good recommendations above.  

I don't see a sample photo eiter.

If you can get the 18-55 to go to f/3.5, you are at the wide end and the 35, 50 and 85 all give a narrower FOV (the 18-55 has variable speed and gets slower as you zoom in). One solution is the Sigma 18-35/1.8 or maybe a 20/1.8. They aren't cheap, though and the DOF isn't *that* short either. If you need a wide FOV with a short DOF, you van stitch a matrix of 85/1.8 shots together as long as the subject matter doesn't move.