[Monkey Wrench]

the primary of the coil should see a pulse. I think of you just put low watt test lamp across the two primary connectors on the coil and crank it you should see your lamp flickering. in that state it will be in parallel with the primary of the coil..

it might be possible to use an oscilloscope to probe the sensor wires for the two sensors and disconnect them to check their resistance. after the DME the pulse should be amplified through a transistor and on to the coil. I bet you could check the input and output of the transistor for presence of that pulse.
in some cars it's called a module, I'm not sure what Porsche calls it. basically the pulse from the DME isn't strong enough to fire the primary of the coil so it's amplified somewhere between the DME and the coil.

someone with better familiarity could likely verify this and maybe help with the pinouts to check.

If you dont have as scope you can check into the downloadable oscilloscopes, you might find one that is Just a free download and uses an input like the sound card. I tried one using an older desktop computer and found it worked fine, that one used the sound card but I don't doubt you can just use a cell phone app these days.

if you want to fool around with those you can just try one there are a bunch if you search for Oscilloscope app. you dont really need to study the wave form, probably just seeing the wave form appear is enough to prove if it is present or not.

I bet if either of those sensors fails to show a pulse to the DME it probably won't start at all or run. If someone has a working car they may be able to verify. I suspect that if the DME sees no pulse you'll have no spark at all , no firing. no start.

from whet I've seen with my Volvo, it may be similar, the TDC sensor is a coil of wire with metal pin through the core. if I hook one to a volt meter without it being connected to anything else, and wag a screwdriver past it, I can see a voltage pulse even with a DMM meter. then you can just take the two probes and compare that to a known good one and see if the resistance is about the same number of ohms.

I'd expect you'd see something like maybe 3000 ohms ,(guessing) .. if the coil is broken somewhere,it could be zero resistance. (open)
if the coil was shorted part way through the bundle it could be less ohms. . Likely the cables are near oil and hard with age, They may get oily and cracked from heating cooling. engine vibration may contribute to the insulation decay there.

if you replaced a sensor you might check the old one like that. Just put a meter across it, see how many ohms between the pins then you can check yours in the car at the connector , same way. If you used an anloge meter (an old style meter with a needle display) youd be seeing the needle wag as the sensor saw its pulses.
Some DMM meters have a little bar representation, you could probably hook that to the sensor with all else unplugged, crank the motor and note some sort of a pulse. the sensor likely has a connector near the sensor and runs to the plug for the DME, if you can sense a pulse at the sensor itseelf, next you can verify that at the correct pins you see the pulse, that would verify that the wire between the sensor's plug and the DME is ok.

after the DME does it's thing it is going to produce a waveforem to be amplified and sent to the coil so you can next verify if that pulse exists.

I think there is a high likelyood the cause of the trouble is a wire got tugged, bad connector, bad ground, not necessarily a failed component. maybe the DME relay is not providing power to the DME.