C_TradeSkillUI.GetProfessionInfoBySkillLineID

[Billtopia]

C_TradeSkillUI.GetProfessionInfoBySkillLineID should always return the full level and maximum level for known skills when called, not just after the Professions Frame has been opened as the frame requires a hardware event to show and the full profession information is only available through that call. You can get information on the highest trained skill (like Dragon Isles Mining vs Shadowlands) through other means but not the "lesser" / older skills. This makes making something like a progress bar for gathering skills a way more difficult process and possible less accurate as you may not even have the current skill level they are at and have to parse the chat message events to find skill ups.