Wheres the sparkplugs on a 1999 alero 2.4 litre engine

I'd start with replacing the Drain plug Gasket. Most conviniontly done with an oil change but you can do it without changing the oil also (Helps to have 2 people)
Also It could be leaking anywhere, (Gravity pulls it down to the bottom of the engine) Thats where I would start. They normally are around 50 cents (give or take) at your local parts place.

Two litres? Unless you are outside the USA, transmission fluid generally comes in quart containers. If you only added 2 quarts, yes, it's very possible the fluid level is low. However, you don't want to add too much. There should be a dip stick for checking fluid level. Run the vehicle until the engine is good a warm, about 15-20 minutes, and then check the fluid level. Add as needed. But remember, don't add too much. Add a little at a time, as you get close to full.

2.4L ENGINE HAS 2 COIL PACKS AND THE 3.1L OR 3.4L ENGINE HAS 3 COIL PACKS

the plugs are located under the cover that runs across the top of the motor i think it is about 2-3" wide,also you might check the plugs to make sure they are getting spark.

OLDS ALERO FIRING ORDER 2.4 ENGINE FIRING ORDER IS 1 3 4 2 THE 3.1 AND 3.4 ENGINES FIRING ORDER IS 1 2 3 4 5 6

On the 2.4 litre engine it is mounted on the cylinder head.
On the 3.4 litre engine it is mounted under the throttle body near the area where the transmission and engine meet.
Both sensors are held in place by one bolt.

YEP ITS THE SAME MOTOR.SHOULD FIT.

top of the head follow the sparkplug wires. if there are coilpacks under them are the plugs.

Just pull them straight up. Twisting will not hurt them. Pop them back on coil tower.

your fans need replacing try hooking them up straight to battery to check if they spin fast its not the fans but the wiring.