Click the "Title Event" tab on your quests. If you don't have the quest to dig it then you won't be able to. Sometimes the quests bug and you have to relog for them to work or appear again. Also leaving the area you're supposed to be in for a title quest will abandon it.
I know it now. I thought I had the quest but turned out I didn'tI did take it tho, and I didn't move to another place, just went to take the weapon needed for quest I'll try relogging
Some of them are just difficult to deal with when it comes to digging things. Have to click on specific areas for it to start digging, etc. All the quests/titles work though, since I have them all.