I have a strange theory that Dawn's father is actually Professor Augustine Sycamore from the Kalos Region. One of Sycamore's assistants in his lab in Lumiose City says that Professor Sycamore learned a lot from Professor Rowan in the Sinnoh region when he was young. Sycamore is also shown to be a moderately experienced Pokemon trainer. This all implies that, at a young age, Professor Sycamore went on a journey throughout the Sinnoh Region and later moved to the Kalos Region. In the anime, Dawn is not shown to have a father, and nobody knows who the father is. Dawn and Sycamore also have similar hair colours and wavy styles. Although Dawn is shown to have a father in the generation 4 games, it is possible that this character is not canonical to the story or is simply a step-father or uncle character. Although it is impossible to confirm whether or not Augustine Sycamore is Dawn's father, it is still an interesting theory to think about.