This command will enable logging of all price changes to the game.log file. The game.log file is located in the "Logs" directory. The logs directory is located in the directory the game is installed to (where victoria2.exe is, e.g. your Steam library). This is a toggle command - run it again to turn this feature off.
The syntax for the debug market command is as follows:
debug market DLC: Hearts of Darkness
Find below working examples of the debug market command.
After running the above command, all game price changes will be logged to the game.log file. Typing the command again will disable the logging.