Hat's off to Geohot
This firmware is confirmed working:
I9505XXUFNB8 (v2 has sorted most of the I9505XXUFN firmware )
Q Does this root trigger Knox?
A Nope, Knox stays 0x0.
Q Does this reset Knox if I already have 0x1?
A Nope. It is still not possible.
Q: Do you have a step-by-step guide how to get this work?
A: Read the OP in the original thread and read the video guide here
Q: Install SuperSU, fails to update binary.
A: check you have root using root checker app.
SuperSU on google play store is out dated and will not work.
See suggestion here by jcagara08
Q: I am getting random reboot after root.
A: Make sure you have remove all knox apps completely. See this by Joku1981