96 saturn sl2 won't start

have the fault codes read first to determine the faulty sensor

yes
try having the fault codes read to determine the fault area
indicates a problem ambient temp sensor, problem BARO sensor or faulty MAF/VAF sensor

Does the check engine light come on? if yes
Could be faulty crankshaft sensor

with smoke mean time to replace engine valve is bad and oil is mixing with coolant internally

You will need to do a fuel pump pressure check. You will need to borrow a gauge or purchase one ($40 to $50), attach it to the fuel injector rail test port, it will have a little black cap on it, turn the key to the run position. Your fuel pressure should be in the range of 45 to 55 lbs.

The knocking noise is a little peculiar, check the engine oil for proper level and smell the dip stick. It may smell like gas, if it does, change the oil immediately. The gasoline has diluted the oil and is to thin, causing the knock.
Let me know.
Regards,

have it scan it could be many things crank shaft sensor ignition coils and module. idle speed control. egr valve could be stuck open.

try getting a small bucket and pulling off the fuel line that runs to the engine and have some one crank the car over and give it fuel to see if anything come out of the fuel line. if it doesnt then eaither a line is blocked or the pump is not working.

do u smell any gas ? check to see if any of the 4 fuel injectors are leaking gas

OK I don't know if this is your problem but my 92 sl2 is kinda the same way. my sl2s ECTS went out and it dose the same this is what it looks like you will have to remove the air duct to get to it and this is were it's located keep in mind there are two of them you want to unplug the one with two wires it is lower on the block. but do not remove it.

after unpluging it try starting your car if it starts them you will have to get a new ECTS Coolant Temp Sensor. btw don't drive around with it unpluged just becouse it runs dosen't mean you should use it like that.

check fuel pump