Speedo does not work , any thoughts would be welcome

The 1998 TDI uses an electronic speedo. Assuming all the other gauges on the dash are working, then it is not a blown fuse. In this case it is either the pick up from the gearbox, the speedo itself or the wiring in between. The easiest way to check is by substitution of the speedo or the pick up one at a time. If this fixes it then the wiring is OK. If it doesn't fix it, then go looking for a wiring fault. Given the age, the wiring behind the dash can fail either by open circuit or shorting, so I usually just run new wires if I get a fault in one.