Title based skills are unlocked by doing quests and/or earning rank in the titles.
You can see all the title skills here
Nightfall
There are not a lot of title based skills for Nightfall
Lightbringer skills 3 skills
Sunspear skills 1 skill
Eye of the North
Now on the other hand there is a ton of skills in GWEN
Asura title track 13 skills…… a handy skill [Air of Superiority]
[Light of Deldrimor] Deldrimor title track 15 skills.. a must have for dungeons
[Ebon Vanguard Assassin Support] Ebon Vanguard title track 13 skills… I use this one a lot
[Raven Blessing] Norn title track 26 skills has some cool skills
