Regarding the coil trigger connection/voltage, I believe the ECU grounds that wire to trigger the coil to fire, so when everything is hooked up normally, you should see no voltage. The voltage will occur only on an open circuit – I believe what you’re seeing is normal.
Since you’ve already swapped coils and plugs, I would move on to injectors as Richard suggested. First swap an injector from 2 or 4 with a good cylinder and see if the misfire follows. If not, check injector trigger signals with a noid light. And if the injector trigger signals are normal, move on to compression and leakdown.