-ㄴ가 stuck onto a noun signals that the speaker is not sure of it: 홍콩인가 갔었는데 (I went to Hong Kong, I think), 18년도인가 갔다가 (in 2018 or thereabouts), 프랑스에 한 일주일인가 (about a week in France, maybe). 어딘가 and 어디론가 have the same vagueness built in and mean 'somewhere'. It is the natural way to hedge your own memory rather than someone else's claim.