Just like you would pull (or short out) a spark plug wire. You can do a similar thing by loosening the fuel injection tubing nut at the injector 1 at at time (cutting off the fuel to that cylinder) while some one is in the car giving it enough fuel to make that sound (with the parking brake on and hopefully the person also has his/her foot on the brake).
When you get to the one/ones that are causing the problem that knocking sound will change/go away and note which one/s is causing the problem/s.
If you find something post here again for further advice.

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84 300D, 82 Volvo 244Gl Diesel