I've seen too many conflicting articles by pros and experts in support of and against the bullet trail in equal numbers that leave this speculation up for debate. I submit that it's not a bullet trail by his head and I'll leave it at that. Note that the nyt does not commit to the theory to stay safe in the reporting.
Images published by the New York Times appear to show a bullet passing by Trump’s head. Following the shooting, he was taken to Butler Medical Center for treatment, according to a report by Pittsburgh-area news station KDKA.