So follow below step by step guide on How to unlock bootloader of LG V10.After that you can follow this guide on How to Flash TWRP recovery in LG V10 and root it.
1.Download and install LG drivers in Your PC
2.Download Mfastboot.zip and extract in on Desktop.
3.Make backup of your data because unlocking bootloader will reset your device
#How to unlock bootloader of LG V10 Easily
1.Enable USB Debugging and OEM unlock option: To do so, go to Settings
-> About Phone -> tap Build Number 7 times to enable Developer
options. From Developer options, enable USB Debugging and OEM unlock.
2.Now reboot your device in to bootloader.And connect your device with PC or Computer.
3.Now open Mfastboot folder where you extracted it earlier and press “Shift + Right click” on any empty
white space inside the folder and then select “Open command window
here” from the context menu.
4.Now type the following command in Command prompt.
See also :How to Flash TWRP recovery in LG V10