pronoun
such-and-such a place; some place or other
Used when referring to a place whose name is not specified or is unimportant, similar to 'somewhere' but with a nuance of 'a certain place'.
彼はどこそこの出身だと言っていた。
He said he was from such-and-such a place.
どこそこに行く予定がある。
I have plans to go to some place or other.
どこか means 'somewhere' in a general or indefinite sense, while どこそこ implies a specific but unnamed place, often used when the speaker knows the place but does not name it.
Compound of どこ (where) and そこ (there), literally 'where-there', used to refer to an unspecified place.