I remember this video about one of the comics, where Imperial intelligence finds word of a "Luke Skywalker" on a planet. It then shows "Luke" wearing sunglasses, trying to get a job running spice, bragging about his victory in the Battle Of Yavin. Vader appears behind him asking, "You claim the name Skywalker?" and right before he tries to say something like "My name is-" Vader force chokes him to death. Did we ever get an identity?
It seems this was his only appearance and he was never named.
The unidentified Luke Skywalker impostor appeared in the comic Star Wars (2020) 5, published by Marvel Comics on August 5, 2020. The comic was written by Charles Soule and illustrated by Jesús Saiz, Arif Prianto, and Dan Brown.