Blender 2.8 - how do I make a texture reflect light? I have a marble texture that I would like to make shiny.  Roughness is currently set to zero, but there is no light reflection.

Any suggestions would be much appreciated.  Thanks in advance!
Diffuse shader is just what the name suggests, diffuse. Try using a principled shader or combining a diffuse with a glossy shader through a mix shader node.:)