OK, the coupe manuals don't show a part like that until '08. Doesn't mean your '04 doesn't have it, just the manuals are no help... Here's the shot from the '08 book:

 

On the g37 it sits on top of the fender liner. I recently replace the passenger side. 2 pins on top and 2 bolts on bottom attached to the engine guard I believe. Might be similar to the g35

 

There maybe? Through that hole in the steel

 

I see 2 holes u can try. The one free one and the one with the push pin. Remove it and sit the piece over it

 

Still unclear to me but that's where it supposedly goes... Here's the "detail" from the '08 illustration, flipped. Doesn't quite line up with the holes you have but notice it is partially tucked behind the fender liner...

 

Imo that detail is insignificant I didn't do that it was jus easier to put it on top.

 

Yeah I gotta just pull the main shield and figure this out. I couldn't see one on the left, by turning the wheels full lock each way. I'll try harder when I do my oil sometime this week. Maybe it goes in the bumber to cover the corner lights harness or something, idk. My guess is even though it's part of the front fender fitting on the parts list, it mounts into a different assembly though if that makes sense. Like doesn't clip into the fender liner.

 

Must sit above this piece where you can't see unless you remove it. Like up in the bumper .

 

No I can def say it doesn't

 

I got it, it was easy with the engine splash shield off. The cut out goes around the sway bar. Done and done. From what I can tell only the passenger side has one unless my driver side is missing

 

Wow, nicely done! I could NOT find that piece anywhere in the FSM... Glad you found the spot for it.

 

Thanks, what a pain haha. I was trying to put in one from outside with the wheel full lock. It will only go on from underneath with the big shield off. Glad that's over. Thanks fo going outta the way to help. I'll try to pay it foward