We bought a 1992 pontiac bonneville. It doesn't start. Changed the spark plugs, new battery. Changed the IGN module and IGN coil. still won't start.

Make sure battery has a full charge. If it cranks good but won't start, have a helper crank it while you visually check for spark at the spark plugs. If spark everywhere, use a gage and check proper fuel pressure and fuel injector pulse.
Any applicable trouble codes? Your obd1, you should be able to check some codes, yourself, if there are any.

Sonds Like A Head Gasket Problem, Do A Cylinder Leakage Test !

The spark plugs receives power to spark from coil pack.Check the power at the coil pack and also check the voltage at the coil pack with meter.If the coil pack shows proper power as well as voltage then its fault in spark plugs.Otherwise its faulty coil pack.The coil pack receives power from battery.so also check the voltage of the battery it should be exact 12 volt.
If the battery shows low voltage then the battery needs to be re-charged.
Then check out.
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crank trigger!

Pull one or two sparkplugs and check them for moisture; not fuel, but for water beads.
I don't know how long your engine ran after losing coolant but there is a chance that you lost the head gasket and have gotten water into the cylinders.

The ign coils should be marked. The front cylinders are 1 3 5 and the rears are 2 4 6..... the coils starting from the front is 1,4 5,2 3,6

Knock sensor will not cause stall, but ign module problem will. Possible you have a bad ign module, but that will be a very expensive guess. Knock sensor is next to the oil filter.

there is a module that the coil pacs plug into, it may be bad or have a bad connection

Your Crank sensor is broken. You have to pull the Harmonic balancer off, it is behind it.

go back to basics check spark fuel etc. fuel probs could be filter or pump. electrical could be coil pack crank sensor ignition module