Undo the wiring connector off the door. Then try to uncover the harness in the sheath you can see. Up to the door pillar. Locate breakage and splice in repair. Not sure if you can get replacement plug and cable so you can splice back in main body of car. Worth searching around if you can

 

Back in my day Peugeot supplied a complete plug and loom repair kit, I suspect it’s no longer available, check with a main dealer?
Lots of stuff on EBay or do what Jonathanh says.

Pardon our interruption...

 

It’s much easier with the door off.
Unscrew and remove the wire multi plug. Two screws that hold the check strap to the pillar.
Two grub screws on both hinges, and lift the door off.

 

As above, very hard to do with the door on. An old thread here from 306OC ....an absolute mine of information.

Replacing 306 Broken Door Loom (306oc.co.uk)

I also think it's unlikely the door loom repair kit will still be available - repair what you have.