number 23 is the spark plug. You can find where the plugs are that way, I did to check out some engine parts too. I can't really say where they are from a real life point of view since I didn't look for them yet.
I finally had time to look for the plugs today, and found them under the black cover with ecotec on it. Take off the four bolts and there they are. thanks for the diagram havik appreciate it.