Which cylinder is which?

Sorry for the newbie question, but how do I know which cylinder is which?
I'm getting a misfire in cylinder #2. Is that the second one from the left, or is that the second cylinder in the firing order shown here?

 

Thanks. 2010, 190k miles. P0302 code. Engine knocking. Coolant level is low. I'm worried about a head gasket failure.

Got it all opened up to access the spark plugs now. I bought a leak down tester on amazon and I'm gonna try to figure out how to run the test on cylinder 2.

Would appreciate any further tips while I got it opened up. Thanks!

 

Is it okay to do a leak down test with the engine cold? I can't really run the engine long enough to warm warm it up.

 

So... First I pulled the spark plugs out, and the spark plug from Cylinder #2 (the one misfiring) was black and oily.

Then, I ran a leakdown test on each cylinder. #1 and #2 were good, but #3 and #4 both leaked around 60%. I listened carefully, and really it seemed like the leaking sound was coming from the same cylinder which was being tested at the time. Nothing from the dipstick hole, no bubbles in the coolant. Am I doing this right? I removed, reattached, and reran the test several times to make sure it had a good seal. I also tried turning the engine down 360 degrees to get back to TDC again just in case I was on the wrong stroke.

I suppose cylinder #3 and #4 are leaking into each other? (even though the sound seemed to be coming from the cylinder being tested rather than the adjacent cylinder?)

Any thoughts on what this all means?

 

That makes sense, but I already cleaned the intake and replaced the PCV valve. Anything else I should try?