There is a brief sequence taking place in a ballet theater where two characters are walking through various rooms with people ranging from preteens to young adults; it is heavily implied that the physical and dance training they go through is purposefully painful. A director makes a young dancer of indeterminate age start over a routine after she collapses, and there are bruises shown on the dancer's legs.
It's two blink and you miss them moments, but a white bug crawls down John Wick's lapel and another two bugs crawl on his cuffs in two of the desert scenes
Several of John's moves involve breaking bones, but they're all quick movements accompanied by a snapping\crunching noise. There are no elongated scenes of breaking a bone, and no bones are ever visible
John Wick cuts his own finger off, it is quick but still gruesome. Another characters finger tips potentially get cut off, but it's so quick and you barely see it that I'm not even sure if I'm right.
Several scenes of elongated suffering (someone being forced to cut off their own finger, someone’s hands being stabbed as punishment, and someone’s back being branded).