Have you checked the sensor on the back wheel for damage also the wiring is ok , & the connector is sound. I am sure this is where the speedo get its signal from. If all looks Ok I would just leave it to your dealer to sort out if you can`t see anything obvious.Hi the speedo on my Suzuki GSXS-s 1000 naked has stopped working everything else works just not speedo
Have checked fuses
Anything else to check before contacting dealer
Cheers
Craig