@jayrob86 this is where it gets a bit complicated if you want to reverse engineer stuff.
The post download scripts are saved on the FOG server, but they are executed by the FOS engine (the linux operating system that captures and deploys images to the target computer).
So to answer your question, the function.sh script is in the init(s) (virtual hard drive that is downloaded to the client along with the kernel (bzImage) when pxe booting).
So you next question may be how can I peek into the inits? There is a wiki for that: https://wiki.fogproject.org/wiki/index.php?title=Modifying_the_Init_Image
The file is in /usr/share/lib/fog (or something like that, its in /usr/share…)