How do we achieve this kind of colour of skin? It would be also great if you could show your methods of selecting skin.

I am not sure this is for DAR Critiques forum but anyway:

This skin is simply bright and pinkish. If the original cloth is what we see, then the skin is easy to isolate as it contains more yellow. But I think they might have done it with the makeup and that might not have been necessary at all.

Regarding the question on colour, the most important really, is to understand how photoshop deals with colours. Reading about the colour channels (red green blue in RGB, or cyan magenta yellow and black in CMYK for example), you will learn how colours are created and thus how adjustment layer impact colour and how to recreate a colour. It will be a handful to grasp, but once you get it, it will make everything else much clearer.

It is not only the colour of the skin that is appealing, it's the colour palette that has been used for the whole image.

Knowing how you get a certain skin colour is not the important thing in the end.
What is important is how to choose the right colours to apply on the whole image, because colour is interpreted by the brain and this very same colour (if you use the numbers for example to apply the same colour on the skin of a model in another image), will not look like this colour, because it will be surrounded by other colours that modify your perception of it.

My advice, read on colour theory (the book i loved about it Johannes Itten : the element of colour), read about how photoshop sees colours and read about additive and subtractive colour wheel. I promise you will never ask this question again.

To know how to get a certain skin (or anything really) colour, you need an image with a colour from which to go, to obtain another colour.

Technically, to answer your question, there are a lot of ways in photoshop, to modify colour. Select the area and use any adjustment layer that allows you to work with colour (curves, colour balance, selective colour etc..).
- to select the skin area :
   - you can draw a mask with quick mask.
   - you can create a new adjustment layer, which automatically opens with a mask, and paint on the mask to select the skin area.
   - you can use luminosity masks (google it, they are amazing).

just hire make up artist to thren the skin model look like it. then shoot.