where to find the folder "/driver/net/"?
The discussion you've been reading is about compiling a modified kernel and a custom ROM for the Galaxy S4, using a replacement wireless driver that's been changed to add support for ad-hoc Wi-Fi networks. The path /driver/net/wireless is a path in the kernel source tree, which contains the source code for the driver that needs to be changed before compiling the new kernel. It doesn't refer to any path on the device itself, or anything else you can change on the device.