You could try to use the Global for TradeskillType Woodworking:
CRAFTING_TYPE_WOODWORKING
Lua Code:
xp1, xp2, xp3 = GetSkillLineXPInfo(CRAFTING_TYPE_WOODWORKING,6);
Judging from the wiki
here Woodworking is not a Skilltype, just SKILL_TYPE_TRADESKILL.