The skylight is NOT able to create specular-highlights on the object. The specular-highlights are of course VERY important to simulate different kind of materials. This is the reason why you should never use only one skylight in your scenes. It is important to have an additional light. If you want to have a very strong specular-highlights like on car paint materials you should use Mr Omni lights (you can find the tutorial of the car paint material in the FDA tutorials for materials). For this tutorial I will use a photometric target area light. This light is very soft, it gives very good and realistic results. Let's create a target area light like in the image below.




It is important to consider that the softness of the shadows of this light will change with the size of the light (big size:soft shadows, small size: sharp shadows).The shadow type MUST be "raytraced shadows", only this kind of shadow will give optimal results with mental ray. Don't create a light with a too big size, otherwise the shadows will be too soft and will cover too big areas, this will darken the environment and will not look realistic. Since now we have two lights you should reduce the multiplier of the skylight. Try to put a value between 0.4 and 0.7. I have reduced it a lot in my scene, in this way it is clear that the main light source is the area light. I like the contrast between strong illuminated surfaces and darker surfaces like in the image below. But at the end it is your taste which will decide about the multiplier amount of the two lights. Sometimes I create an additional area light on the opposite side of the first one.

If you like to have more than one area light you should disable the shadow of the light with lower intensity. Too many shadows are confusing and really ugly in a rendering. Make a rendering. You should have the result like in the image below.