Is there an addon that simply shows me which titles I have and don’t have and tells me roughly how to get them?
Basically a mount collection window but for titles
No addon or Wowhead tool that I’m aware of, though I think every single title is associated with an achievement.
If the “Title Completionist” addon were simply based on tracking the correct set of achievements, it’d likely work.
Check out AllTheThings, among … all the things that it does, it has a Titles sub-section that gives some info how to get the ones that are missing.