I think you have to talk to Haskell 1st to give you a list of trinkets that you can get. It usually gives herb of grace after getting the trinket but if this is the 1st time, you should talk to Haskell 1st
You need to get the devil's snare 1st to proceed. If you don't know how, get the minotaur essence then go to the lake. You'll be able to unlock Lothar's quest as well as the trinket
In the rolling stone quest, side with Sebas about him kicking Lothar in the balls then finish the quest normally. After the next day, there will be a new choice from Sebas at the shop. You'll unlock the 4th cg