Do you mean for the classic profession level progress bar?
    For the full window, see Wow_CqWTJFEMt5.png file, it will be Dragon Isles. Do the following to change:
    1. Go to Professions (k)
    2. Click the Profession
    3. Click Filter
    4. Click the profession type you want, i.e Classic 
    That will show the current profession level but it is not permanent, the filter will reset when you /reload / exit game / log out / log back in. It will reset to the highest expac profession learned, for me it will be Dragon Isles.
    After logging on to a level 24 character and learning professions esp classic, any addons or weak auras that display professions level bars will show the highest expac profession, so, if you learned Classic <name of profession> and then learned Outland <name of profession>, Outland will now show in the bar. This is regardless if you learned 300/300 or 75/75 of the previous one.