So if it's "at least one", i see no problem that players character knows more than one place - if it makes sense.
As a rule of thumb I allow up to 3 if terrain is Easy or Moderate and it's Free Land or Borderland, up to 2 if is Hard/Severe in Wild Land and only one in Daunting terrain and/or Shadow Land/Dark Land. If it's players homeland or he has Region-lore speciality in this land, I may lower the prerequisites (but still no more than 3)
For example, I agreed that Mirkwood elf Wanderer in my party knows three safe places in Woodland Realm (Severe but Border Land and homeland), which is one of hers Known Lands. She is from there, she has some friends, she knows the paths, places to stay and the land is relatively safe.
She also knows two safe places in Western Mirkwood, but only one in Grey Mountains Narrow (she could know one more, but the player decided that her character knows only one at this moment) and one in Mountains of Mirkwood (because it's Dark Land and Daunting terrain).
Until now we have discussed most of such places, but we left those locations in Grey Mountains Narrow and in Mountains of Mirkwood for later. When the time will come, and party will be planning their journey there, I will ask her to describe them and pinpoint their location. And no, I do not fear any powergaming, from players side (like picking very convenient location etc.), but if you like to have such matters discussed in advance, you can totally do this - whatever suits your style of play
BTW it's worth to mention that the hex map is for LM and the player's map is the plain one. Step one: Embarkation in Journeys chapter explains, that the players are planning their journey on Player's map and the Loremaster consults the route with his. Of course more experienced players know which land is safe/dangerous and easy/hard to traverse, but from our experience we know that is more fun to plan the travel route on plain, more in-game map
But yes, since he is Wanderer and he Knows that Land, you can give him hex map to pinpoint hex, that will be certainly more convenient.