When On the Road premiered in Cannes in May, there were reports of multiple nude scenes from Kristen Stewart, including a scene where she is clearly topless while her character is giving a double hand-job in a car. When the North American version premiered at the Toronto Film Festival, any nudity from the car scene was cut. Fortunately there are clips from the French Bluray version that comes out on October 17 available, and all the Kristen Stewart nude scenes that were cut are still in this version. Alice Braga and Kaniehtiio Horn are also topless in the film.
Here is a brief review that Salamar from Celebfans posted back in May after seeing the film at Cannes.
Alice Braga is topless
Kristen Stewart is topless, first in a brief scene where she is in bed but it's dark
Then sex scene on her back brief too
Then the infamous car scene where she masturbate both her costars, also brief
Finally in a sex scene with Sam Riley a long look at her boobs from the side.