This is set up in the Multipass Manager. Full documentation can be found here.
See also 'Compositing Vray Layers in Photoshop'.
Beauty Pass
Subsurface Scattering (SSS) +
Caustics +
Self Illumination +
Atmospherics +Specular +
Reflection (Raw Reflection x Reflection Filter) +
Refraction +
Lighting (Raw Light x Diffuse) +
GI (Raw GI x Diffuse)