Some devices are rather easy to root as it just requires you to unlock the bootloader, flash a custom recovery and then follow that up with your root solution. Others can be more complex and so detailed step by step guides are incredibly helpful. XDA Member hikari_calyx recently took the time to write an entire guide for how to flash a custom recovery and gain root access to the retail Nokia 6. So far the OP has only tested this on the D1C/TA-1000 variant of the Nokia 6, but says that in theory it should work on any variant.
How to Root the Nokia 6
XDA Member hikari_calyx has taken the time to write up a complete guide on how to flash a custom recovery and gain root access to the retail Nokia 6.
Nokia 6