read specular and specularitymask https://docs.unrealengine.com/udk/Two/MaterialsShaders.html#Specular
Specular
With this, you can blend an EnvironmentMap on the Shader: set a TexEnvMap texture in Specular and the Shader will look shiny.
You can also add a SpecularityMask, this is a texture with an alphachannel, or a masked texture, that tells how shiny the Shader has to be in each pixel. The black parts of the alphachannel leave it mat, and the white parts become the shiniest. Of course, the SpecularityMask doesn't do anything if you didn't set a TexEnvMap in Specular.
This is a Shader with Specularity on it, and the SpecularityMask is a white alphachannel with a black circle in it:
SpecularityMask
This Material is used in conjunction with the texture assigned to the Specular field. The SpecularityMask uses the alpha channel of whatever texture or Material that is assigned to it and uses it as a mask for the Specular field.