An N frame .357 Magnum revolver.
Based on your lack of description, 100-1000 USD.
The "J" frame is the Smith & Wesson small frame revolver such as the model 36 .38 special. The smallest frame, as in the model 36 Chief's Special.
A K frame revolver.
I frame
Medium
It is on the frame.
Frame, barrel and cylinder
Yes, a model 66 is a K frame revolver.
100-800 USD depending on condition, accessories, box, tool kit, manual, etc..
On the underside of the frame
On the frame and the grip frame.