What are the literary methods used to present conflict of identity in Frankenstein?
I believe that by questioning "literary methods," the question refers to how the story is written. Mary Shelley's Frankenstein is defined as a multiple narrative. A multiple narrative is a text where the point of view changes over the course of the piece.
Essentially, the tale is told by Walton (the man in search of magnetism at the pole). Walton's crew has been joined by Victor Frankenstein. Victor, fearful of what he has done, tells Walton about his "monster." In an attempt to keep Victor's tale as close to the truth as possible, Walton retells his tale. That said, when the story turns to give the monster's point of view, it is told through Victor's recollection and Walton's retelling. Therefore, at the most complicated point in the story, three voices are speaking (Walton telling Victor's recollection of the monster's story).
This method of narration presents a conflict. One could state that many things could have been lost in the telling of the tale. Readers are not really getting the story from the monster's point of view. In "reality," readers are not getting Victor's story from his point of view either. Instead, both Victor's and the monster's stories are being told by Walton. Many times, by the time the tale turns to the monster, many readers have forgotten that Walton is the one truly narrating.
This causes readers to lose their connection with who both Victor and the monster really are. Instead of offering true first person narratives, Shelly gives readers three different stories from one point of view. Much could be lost. Therefore, readers could justly state that the characters presented are those of Walton's making. The conflict of identity, then, lies in the "fact" that each character is not telling his own story. Each character, Victor and the monster, must rely on Walton's ability to recollect what was told to him. Identities for both Victor and the monster could be altered by Walton's memory of the tale.