You can now easily root the Korean variant of Samsung Galaxy S6 running on Android 5.1.1 Lollipop using Chainfire recognized Xda developer cf-auto root method.
You can follow the steps below to root Galaxy S6 SM-G920K. Note that using cf-auto root will trip Samsung Knox counter and voids device warranty but it is always to gain root access and have super access to your Android.

Galaxy S6 SM-G920K
Pre-requisites:
How to Root Galaxy S6 SM-G920I:
Here is how to root Galaxy S6 running on Android 5.1.1 Lollipop firmware.
Step 1: First of all, download and extract/unzip the required files mentioned above.
Step 2: Run Odin3 and leave the default settings.
Step 3: Turn off your device and reboot into download mode by holding and pressing the Volume down+Home+Power keys simultaneously till Android warning sign appears on the screen. Hit Volume up to continue.
Step 4: While in Odin mode connect your device to your PC.
Step 5: Hit the AP/PDA button and select the CF-Auto-Root-zerofltektt-zerofltektt-smg920k..tar file.
Step 6: Click Start to flash the twrp file.
Step 7: When completed, Odin will give Pass! Message and your device will automatically reboot.
Congratulations! You’ve successfully rooted Samsung Galaxy S6 on Android 5.1.1. You’re now a few steps away to install any Custom ROM and Recovery of your choice.
Don’t forget to share your experience in the comment section below.
Hello, I'm Imran Aftab, a tech enthusiast using Android, iOS, and Windows. Hardware expert for Gaming & Crypto mining rigs. I have been writing on tech since 2013, starting with ohguideme, then Androidcentral. I have written and published several guides and tutorials on how to root Android, flash custom ROM, recovery, and jailbreak iPhone, and have written several guides on how to bypass FRP. I also worked in a phone repair shop, so I have pretty good experience with mobile software and troubleshooting. So, all the guides you see here have been tested and confirmed to work.