C:\Users\YourComputer\Documents\my games\Sid Meier's Civilization VI\Logs
firetuner for VI is not out yet, but the one for V worked for somethings.
If you don't have it, you can look on steam- click on library - tools and look for civ v sdk
If all your doing is using it to monitor lua output, there isn't much you need to learn. Just start it, it should connect to game, if not there is a connection option at top.