Expending some XP in it should be enough. An experience point in "freaky magic XXX" should be enough to start investigating that kind of magic (and generating more XP in return). You would need a learning source to do so. So yes, invrstigating stuff inthe lab would count, as would be learning from a practitioner, reading about it et al. An XP source
I tend to be a little more lenient. If a character has encountered the magic in open play, that's enough for me. If the character has an Ability (such as Magic Lore) with an appropriate specialty, I might give the benefit of the doubt. And failing that, if they make a Magic Lore roll against an Ease Factor dependent on how rare/exotic the magic is then that's also enough for me.
I'm always looking for ways to help the players get what they want and I think that little lot should enough opportunity.
Read HoH:Soc about the Pralicians, as these sorts of magi need this very knowledge to use Vim against it. Rules say that Magic Lore covers the magical stuff and Organization Lore covers the who's-who and history, traditions, those sorts of things.
Now I don't feel it is mere enough to have seen this thing once. If you observe a practicioner over time, use counter magic against it (like Winds of Mundane Silence being the generic catch-all spells, and also bloody hard compared to Unravelling) or search or loot their lab/workshop/witches kitchen may be enough. Or reading their minds even!
But this is a soft rule. A hard rule could be to also require the magus in question has spent at least [X] experience points on a relevant ability (or spell mastery?). This can be from Adventure, Practice, Exposure, Teaching/Training (for a willing hedgie, or perhaps not - ReMe can do many things...).
And then the SG or Troupe needs to decide on the value of [X]. My oppinion is for the 2-5 range. It needs to be significantly less and much easier than what it requires to obtain Insight for Integration, which is a season of study/activity and a Int+Magic Theory vs. 18 (IIRC?).
Or maybe not, if you want it to be hard, then require this! But to be familiar with the 10 Hermetic Forms only requires you to have the Arts Opened. No roll, nor requirements form the master per se (well, any Art below 5 results in a Defiency). An apprentice just past this point can after all use Hermetic Magic.
But the idea of needing a score in 1+ in the relevant tradition's equivalent to Magic Theory seems plausible. A season or two of effecent snooping could lead to this.
For me, having a relevant Ability Score of at least 1 is the basic criteria.
So, if dealing with a hedge tradition, then a score of 1 in that tradition's Magic Theory (or some other relevant Ability for those that lack a formal theory). If dealing with creatures, then the appropriate (Realm) Lore would be the obvious Ability.
However, as ever, it depends on context. If your magus has no Folk Witch Magic Theory Score, but a folk witch lived in his covenant for 10 years --- then that would probably count as "some knowledge".
My immediate thoughts - these may hange upon reflection
That kinda depends:
If you learn about a tradition (we'll take gruagachan as an example) by studying the results of their magics, you'll learn about what you see.
You get a few people that have been granted blessings via GiBl effects and keep the in your lab for a season or seven, while you try to figure out what's going on there. You'd learn about Blessing only.
You get hold of people affected by a variety of effects and study them in the lab. This should take more time, but provide wider insight, probably into the whole tradition (well, the magical aspects anyway).
A friendly (and perhaps foolish) gruagach teaches you about the principles of his magic for a season. You might have to mull that over for a bit longer and you might have to invent the first PeVi spell using experimentation, but that's about it.
You catch and tie down a Guragachan (or sneak into his hut while he is sleeping) and cast Peering into the Mortal Mind...What do you get then?
Good points all of them.
Perhaps the Insight mechanics could be used? That horrible Int+MT roll vs. 18 which only experienced and focused magi don't fear. If succesful after studying some source you get "the full picture" otherwise you just get a glimpse, good enough for understading one of the Hedge Arts - like the Blessing.
Well I'm off to find me a witch to study, and then we'll see how things turn out. If it's too easy it's not fun! But then again neither is too hard...