noun which may take the genitive case particle 'no', adverb
somewhere; someplace
Interrogative word used as an indefinite pronoun or adverb, similar to どこか but with a slightly more formal or literary feel. Can also be used attributively with の.
See also: どこか
どこぞで会ったことがある気がする。
I feel like I've met you somewhere before.
どこぞの国で起こった出来事らしい。
It seems to be an event that happened in some country.