I suggest you connect the MK808B with your TV and your laptop together, so you can root it easily; we already tested to root MK808B sucessfully with the following method:
Use the DC port to power on the MK808B, and use the OTG Port to connect your MK808B with your laptop.
1) Download Moborobo and unrar into a folder.
2) Download TPSarky-VonDroid-Root.zip and unzip into a folder.
3) Install Moborobo and open it
4) Make sure USB Debugging is enabled on your MK808B ( you should go to “setting” –”USB”–choose” connect to pc chooice” and then go to “Developer options”–open”USB debugging”choice)
5) Wait for Moborobo to see the device and install drivers. It will detect the device as MK808B.
6)Run TPSparkyRoot.bat and follow the on-screen instructions.Your MK808B will reboot 3 times during this process.(please remember, after each reboot, you should choose “connect to pc” every time in the MK808B, if not, the root will be failed, that’s the reason why ask you to connect the MK808B with TV and laptop together)When complete move on to the next step. (this root tool is based on the window n101 tablet, but please don’t worry,it can use on your tv stick, because they are the same chip)
7)Install SuperSU from Play Store.(If not installed in previous step)
8)Optional Install BusyBox from Play Store.