It's in Japanese, but basically those requiring 50 kills,1000 kick etc., will be account shared.
That being said, notable ones are:
Neck grabbers ( rip hardworking kais)
All niflheim titles
Confirmed Thousandaire and ALL niffy titles are shareable. Confirmed all Neck Grabbing titles are NOT shareable.
For all us Evie out there, Brain Freezer is NOT account shareable.
All labyrinth titles are shareable. Char specific labby titles are shareable too but not with everyone else, they get shared to identical chars sitting on one account (ex: I never liked Evie won't show up on a Lann, but if you have 2 Evie and your other Evie never touched labby, you'll see it on her. This rule also applies to the doppleganger titles, they will only appear on the chars that can actually attain them normally).
Transformation titles (Path of Duty/Honor) are NOT shareable.
Crimson Blade Youth and Crimson Blade Mercenary are shareable. Certain equip set titles that are char specific are shareable between the chars that can actually attain them (ex: Queen of Roses will show on Evie and Arisha but you won't see it on anyone else). ***Elite Commander breaks this rule as my Evie has it. All other equip set titles were made available in Aislinn's shop like a year or two ago.
NO Ein Lacher, NO expertise.
Free Match titles share, total of 9 of them.
Tieve's Helper and Gwynn's Helper share. Untrustworthy and Trustworthy share. Rag Doll Provider and Wooden Doll Provider DO NOT share. Hakam's Successor and Hakam's Apprentice apparently DO NOT share either.
Certain event titles share. Apparently 1 per account titles do not share while 1 per char event titles share. ***Glittering DOES NOT follow this rule, there may be others... You will however see Angling for Love, Master Baker, Bear Back Porking, etc. No Brilliant!, no 90 MPH, etc).
Thank you to all my friends that helped piece this information together. If you want me to give credit by naming ya let me know or just comment, you know who you are. I maintain privacy until told otherwise
Edit: All Abyssal Arena titles NOT shareable EXCEPT the last one "The Greatest of All Time 30/30". That ONE title is shared.
Nemain clear title "Epidemiologist" is account shareable.
Fishing titles are shared fyi, no need to keep catching Tahtichs or 50 of the same kind of fish on every char.
Alban Festival titles "Spear Master" and "Wall Master" NOT shared.