I'd look into what each Gild stands for, what archetypical members would spend their time doing.
However as the Gilds are a political organization I see a lot of overlap with Order of Hermes Lore, Code of Hermes, Intrigue etc.
Most of not all Gild training is done at Duremar so Covenant Lore seems relevant here. Elder and Hawthorne training might be at Irencillia or Crintera respectively, most likely for magi of Houses Merinita and Bjornaer respectively, however these magi may very well already have spent their entire apprenticeship there.
*Oak Gild are IMHO conservative and resist change. They would want to know the history and legal affairs of the Order and use it to influence or pressure their political opposites. Order of Hermes Lore, Code of Hermes, Intrigue, Leadership comes to mind here.
*Linden Gild are peace-striving diplomats. They could use more or less the whole array of social abilities: Intrigue, Folk Ken, Guile plus Artes Liberales, Charm, Leadership for the whole package for the Debate mechanics.
*Appel Gild interact much with mundanes. Apart from social abilities they could benefit from mundane knowledge of the organization of nobles and trade guilds. Plus spells and Mastery (quiet, still) for discreet magic, perhaps Mentem and Imaginem,
*Ash Gild are aggressive and active. I can see then teaching Penetration, perhaps Parma Magica depending on how you interpret how it is taught, Concentration, Finesse. And perhaps combat spells and useful Masteries.
*Elder Gild focus on faeries. I see them teaching Faerie Lore, Faerie magic but also Etiquette and other social abilities to interact with those kinds of faeries.
*Hawthorne Gild focus on the wild, unspoiled magical areas. I see them teaching Magic Lore, perhaps some relevant and useful Supernatural Ability is the magus posses it. Maybe some aggressively-useful arcane abilities or magic. Maybe some Bjornaer abilities if of that house, like Heartbeast.
IIRC Metacreator has some non-exhaustive list when choosing Gild Trained virtue which is different from Gild to Gild. I didn't look it up but my list above is likely inspired what I remember.
I currently play in a Rhine saga but I did not choose Gild Trained.