I'm not Blarfnip but, my config file is in the folder where jrnl installed itself. Seems like by default, it is (Drive:)\Users\(Username)\AppData\Local\Programs\jrnl; the file itself is config.json. You can also take its shortcut and Open File Location
Notifications also don't work for me no matter what time I set tbh, so I just have an alarm on my phone for it