Search the ESO sources for SKILLS_DATA_MANAGER
https://github.com/esoui/esoui/blob/...atamanager.lua
It provides functions to check for some skilLines
And there exist API functions like these in the ESOUI documentation txt file:
GetNumSkill*
GetNumPassiveSkill*
GetSkill*
GetProgressionSkill*
GetSpecificSkil*
IsSkill*
The skill lines (e.g. Werewolf, 1hd, staff, etc.) got an index: skillLineIndex
and the skills at the skill line too: skillIndex
Hope this helps