I’m trying to create guitar. I’ve created very reflective material, but still can’t achieve something like this:
I think this might work for you if you put some reflectors around your scene. The reason the top guitar has a nice white reflection on it is most likely because of that. I would create a plane with a gradient map on it bit enough, and place it so the reflection shows up when viewing through the camera. 
I can’t get the feeling out of my head tho, that there is still some roughness in that reflection, otherwise the reflection of that HDRI map in the background would be crisp and clear… But, that said, I also think that the wood under the clearcoat should be a bit rough, so in the principal shader node just add some clearcoat to the mix and i think that will bring out the nice crisp reflections more as well…
If you don’t mind sharing the file, i could look at it a bit and figure out what’s going on a lot better.
P.S.
Are you using this in a lo-poly situation? I noticed the polycount on the shape of the guitar is kinda on the low side.
The top of the electric guitar is unlikely to be a totally flat plane which obviously has an impact on reflections.
I agree in that there appears to be a high roughness value somewhere in there. Maybe roughness is still hiding in the Specularity or Clearcoat Roughness settings(?). If you’re using a texture to provide a roughness factor, perhaps try a color ramp to adjust how much of the texture has influence. Can you provide a screenshot of just the node setup? I agree with @cet77 in that the HDRI should be crystal clear if roughness values are zero.
I agree with @cet77 and @JohnMalcolm1970 that it’s a reflection plane. I made something quickly to illustrate it. On the right is a 13m 30W Area light. Just remember that most of the effect is because of controlled lighting (no HDRI) and the bevel. There is a nice bevel to the electric guitar that’s not present in the acoustic guitar.
What do you mean by “reflectors”?
Well, pure Principled shader with 0 rough looks like this:
Here’s the .blend file: https://drive.google.com/file/d/1lTZBUf43RqP7oUI75UHZ3yMo2RLJdp7P/view?usp=sharing
Having something that’s not completely flat really does help for stuff like this. I did a guitar a while back. I’m at work so can’t fish out the material, but it comes down as much to the shape as anything else.
I can’t increase polycount since I’m creating mid-poly model, not CGI
@vefery - Understood about the roughness values. Hard to know exactly without a few more example files. But no worries . . . glad you’re getting some help. Love this community for that. Render on! 
@JohnMalcolm1970 - Gorgeous guitar!
Ok, I’ve managed to achieve this:
Still a lot of work to do, but at least I’m moving in right direction
That’s okay. I was just curious… But i found the problem in your material, or not so much a problem, but a consequence of using a bumpmap on the body. A bumpmap is kinda like roughness. It makes the normals of the surface appear bumpy, and that takes away the nice smooth shiny feeling you get when something is polished. So what you can do to remedy that is basically using clearcoat. I saw you already did that, but the effect drowned in too much specular reflection, so i dampened that and increased the clearcoat to 2, also decreased the bumpiness to 0.2 and added a reflector/plane-with-emission into the scene… I did it so the reflector object only affects the glossy pass and not the others… (those settings are in the object tab under visibility/ray-visibility.
I’m sending the file back with some small changes. Maybe that helps a little. Just need to upload to gdrive… i’ll post it here when it’s done… 5 minutes or so…
edit:
Here is the link
Ah, also forgot to say that I made the changes in blender 2.8 latest build. I don’t know whether or not you use that, but If you were using 2.7x the procedure is mostly the same i believe.
Try playing with fresnel.
The image you have presented is 90% done in photoshop. whole guitar gradient as a reflection overlay, and then cut in one place. You don’t see reflections like this in real life. It’s added later to look cool.
Although there are some things you can change.
With studio lighting you can see what’s influencing that.
Being able to have a separate clearcoat normal and roughness can be amazing for creating “quilted” or “figured” wood often seen on guitar tops.
You should pay attention to how the wood appears prior to clearcoat. Roughness and bump. For the clearcoat, if the underlying had any significant bumps after sanding, you might want to have some of these show through - think something like topcoat bump = 1-5% of the underlying, then on top of that add any bump scratches that are only visible on the coat, and on top of that any large frequency random noise to disturb a fully flat coat which is not realistic.
For a mirror like polished topcoat surface finish, consider sharp glossy or at least very low roughness. If you go with roughness map, it should only be for imperfections, scratches, and fingermarks etc. Can coat roughness be mapped now? I haven’t tried lately but it was buggy, requiring a separate glossy node for topcoat.
If you go for a thick epoxy/resin like coat, consider darkening the underlying diffuse at glancing edges. A high IOR coat value (1.75-1.85 iirc) doesn’t cut it as far as “darkening” goes. It’s not the IOR that causes the darkening, but the thickness.
