so if the above suggestions didn't work.. and if you're really sure your quest got bugged, here is how to find the .que files:
btw, quests usually get bugged if you played on multiplayer and someone not on your party completed it
as i remember, it should be somewhere My Documents/My games/Titan Quest
inside there should be folders named Titan Quest, Titan Quest Immortal Throne, and maybe one for ragnarok? maybe Titan Quest Ragnarok?
but the right folder should contain folders named like your character names.. iirc it's inside Main/Save Games.. if you find a folder with your character name that got bugged, open that and there should be folders named normal, epic and legendary.. inside those folders are the . que files.. the file names are just jumbled letters and numbers with the extension .que
make sure that whatever you delete, you back it up first
so if the difficulty that got the bugged quest is in normal, open the normal folder.. change view to "by date".. if you remember when it got bugged, then it's easier because you just find the que file with the right date.. if it's your last quest, choose the latest date.. whatever que file you delete should be deleted in game when you enter your character.. if it's the wrong quest that got deleted, it's going to be trial and error so it's a pain in the ass
but hey koderkrazy made this post before:
https://titanquestfans.net/index.php?topic=514.msg5276#msg5276it's not clear but the quest is given sometime near the warrior princess quest right? i see the warrior princess quest there at the near bottom.. so maybe you could narrow the choices