Normally the Vá speedometer sensor installed at the top of the gearbox, near the wall that separates the cabin engine, but in this specific case I would not know how to tell you more accurately where it is.
Anyway, one thing you can do is approach the Peugeot and ask for a copy of the explodes where the speedometer sensor comes out. There it will be in the figure where you are installed exactly. (And by the way you buy it).
All the best.