Even though your local Infiniti dealership is a POS you didn't need to spend that $125 since it's under warranty! Good recovery on your own though....
Gary

 

2006 G35, cooling fans not working, found 3 relays behind battery, which one is the high speed, I dont have a manual.

 

You can get a service manual here:
https://www.nicoclub.com/infiniti-service-manuals

 

It's sort of convoluted the way those relays work, if the first two are BOTH ON then it's low speed, if the second two are BOTH ON then it's high speed.

Just buy one relay to start with, write on it with a sharpie to identify NEW and the existing 1, 2, 3, put it in the lowest position to see if it turns on high speed (you can force the system to high speed by turning on the AC), if it doesn't then swap it for the other two positions. Then you can isolate the bad relay.