This is most likely etching (corrosive damage to the surface removing the shiny layer) from the acidic coffee. Granite is not easily etched, but it is definitely possible either from a very strong acid or from repeated exposure to acids especially if the granite is several years old.
The other possible issue is a film of hard water deposits, but I doubt it. Typically, hard water will have a whitish color to it rather than just looking dull. Do you have hard water or notice any similar dulling around the sink?
Again, most likely etching. Since granite is so hard, there is no DIY product for restoring the shine. You'll need to call in a stone restoration pro to re-polish the area.
Avoid future etching by using a decorative tray under the coffee maker or be very diligent about cleaning up all coffee spills immediately in the area.