These are two very missable achievable, but Conversationalist is the only achievement you need a new game for.
Conversationalist is best down through a guide and a speed run (I did it last with a speed run in only a few hours, yes I'm fast). Basically you can either follow and trust a guide in talking to lucy or you can just keep trying to talk to her until she tells you to go to bed or sleep, something like that.
With Hungerer of Knowledge, you can start a new game and just make sure you get every glitch in the assassination scenes and talks with the assassin leader (forgot his name) or you can replay certain assassination blocks and there have been some reports that it counts as it is 85% of the total 100% of glitches counted.
Hope I helped,
Elder scrolls IV: Oblivion
Elder Scrolls IV: Skyrim
Games currently working on
Dead Space 2
Assassin's Creed III