Meanings
so-and-so, this or that, (a) certain (one); used to stand in for definite referents that were specified in a different speech context, and whose specificity in that context is highlighted in the current one, but whose actual identity is not relevant in the current context.
Er meinte dann zu mir, dass ich doch einfach den und den hätte fragen können, oder in dem und dem Buch hätte nachschlagen können.And he told me that I could've just asked so-and-so, or looked it up in this or that book.