which Nikon lens is for best sharp portrait shots?

It has the POTENTIAL for sharp pro looking pictures. But the reality is up to the person using it.

Here's some examples of a shots taken with a Nikon 50mm f/1.8http://www.flickr.com/groups/nikkor50mm18/pool/

http://www.flickr.com/search/?s=int&z=e&w=all&q=Ni...

The best lens for portraiture are the Nikon 85mm lenses. If you are using a Dx camera, simply backup a bit - which should not be a problem in a studio setting.

This video presents an argument that a 50mm lens is not a good lens for portraiture:

http://www.youtube.com/watch?v=nG1pN5Vic8E

It is debatable whether a 50mm is the best or not for a Dx camera, but for a Fx camera, there is no question that the 50mm is not the best.

And some pros have been going to a 70-200mm f/2.8 as it presents outstanding bokeh.

It can't exactly guaranty that, because there are user factors that go into the result.

However, if the right things are done, then the lens should do its part very well.

I think 50mm on DX is a bit low for portraits. It has the angular field of a 75mm on FX.

A possibly better choice is the 60mm AF-S f2.8 Micro Nikkor.

All.

No guarantees. Sharpness is the responsibility of the user. Bear in mind, the 50mm f/1.8 is a great lens to use for blurring purposes!