It's hard to find a picture but here is the speedo parts diagram:
https://www.fowlersparts.co.uk/parts...r-sv650ak7uak7
Part #22 is the speedo sensor and it sits on the left side of the front forks.
This picture, for an "N" model unfortunately, shows the speedo sensor within the headlamp and a (basic) method of testing the sensor.
https://www.manualslib.com/manual/80...age=408#manual
The bit that breaks that people have referred to looks like this:
https://www.manualslib.com/manual/80...age=289#manual
Showing installation:
https://www.manualslib.com/manual/80...age=292#manual
The part changed over the years from a 4 segment to an 8 (?) segment rotor - not sure when it changed (Bibio knows).