941 cat started knocking

That would be a D330C engine until s/n3884 then 3304 engine.
First thing to check would be a bad injector (makes knocking sound) by finding which cylinder is the culprit then move that injector to another hole to see if the knock follows.

how do i go about finding which one is bad though?

Get a stethoscope (you have one in your toolbox called a long screwdriver) and listen in the vicinity of each cylinder in a couple of different places (next to injector, down side of head, top of block) to determine where it's loudest

You could also loosen each injector pipe one at a time too

If its a bad knock, remove the oil filter and cut it open to see what is in the pleats, I agree it could be an injector and you should be able to tell by swapping them around to see if the knock moves with them, but too much messing around trying everything is pointless if a bearing or piston is already breaking up and getting ready to launch itself through the block.

I always thought that you shouldn't use ether on a glow plug engine--is this because a hot glow plug will ignite the ether or because the precom chamber accumulates all the ether in a small space and creates a very pressure??

ill find me a long screwdriver and listen tomorrow, i loosened all the lines going to injectors one at a time and couldnt tell that the knocking went away, they all was spraying out diesel and could tell it was making the engine miss i guess you could say. i cant really hear the knock when idling but gets louder the more throttle i give it.

I always thought that you shouldn't use ether on a glow plug engine--is this because a hot glow plug will ignite the ether or because the precom chamber accumulates all the ether in a small space and creates a very pressure??

ill find me a long screwdriver and listen tomorrow, i loosened all the lines going to injectors one at a time and couldnt tell that the knocking went away, they all was spraying out diesel and could tell it was making the engine miss i guess you could say. i cant really hear the knock when idling but gets louder the more throttle i give it.