My speedometer isn't working, Do I need to take to dealer or can I take to local mechanic? 2004 sedan g35

 

There's a few components, the speed sensors are located at the rear differential, it's a magneto-pickup style, I would have it inspected for damage first to make sure something isn't visibly damaged. The combination meter can fail also though, the easiest way to check would be to use an OBD2 scanner to see what speed the computer is sending while you drive. If the computer is reading the right speed then it's likely the combination meter, if the computer doesn't show you moving then it's probably something with the speed sensors on the diff.