Is 다른 곳에서 본 natural when I just want to say simply "Seen Elsewhere" only? This is the translation in most translating apps (like google translate & Papago)
다른 곳에서 본 is grammatically fine but it sounds a little too specific and dry (and a mouthful to pronounce). You could shorten it to 다른 데서 which sounds smoother (데 and 곳 are equivalent but 데 is easier on the tongue, and 에 is usually dropped after 데).
I think what is more often said than either of the above is 어디선가 본 (seen somewhere) though. Even in English, "Have I seen you somewhere?" is probably as frequently heard as "Have I seen you elsewhere?". In poetic language in particular, it might be a better choice than 다른 데서 본. For instance, there is an old song which has the line "언젠가 어느 곳에선가 한번은 본듯한 얼굴" (a face I might have seen once somewhere, sometime), where 어느 곳에선가 is just a longer version of 어디에선가 (어느 곳 = 어디). 어디 has a more open and unresolved feel than 다른, and is thus more conducive to poetic feel in my opinion.
어느 곳 and 어디 are a questioning word like "where?" (지금 어디 있어? = Where are you now?), but in a non-question sentence they mean "somewhere" (most question words in Korea work like this).
Also note how 어디선가 is constructed.
- 어디에서인가 (full form) = 어디 (where) + 에서 (in/at) + 이다 (is) + -ㄴ가 (questioning suffix) => "where was it?", a clause-like form which has become a questioning adverbial phrase.
에서 usually contracts to 서 after a vowel-ending syllable (but 곳에서 doesn't because of ㅅ), and similarly 서인가 becomes 선가 (인가 -> ㄴ가). So the shortest and most commonly heard form is 어디선가, although 어디에선가 and 어디에서인가 are also fine.
(In everyday speech, we more often use the even shorter form 어디서, but in a text or narration, 어디선가 is probably better.)