Which rhetorical device is exemplified in the following passage from “frederick douglass”?

. when it belongs at last to all, when it is truly instinct, . .; when it is finally won . . a. repetition b. parallelism c. exclamation d. metaphor

This is a parallelism.

Parallelism is the repetition of the same structure, typically grammatical structure, throughout the text.

Here the repetition is of 1) the words "when it" and 2) of the present tense, 3)  third person that follows it and  4)each part has as adverb, such as "finally" - there are 4 characteristics which are repeated.