The following is a brief description of the chapters in His Juliet that most heavily feature self-harm/thoughts of self-harm. This list may not be fully comprehensive of every mention in the story, but these scenes are the most prominent ones.
Chapter 29: Brief and vague mention alluding to what Juliet did in the past to cope with hard emotions.
Chapter 33: Juliet doesn’t want Romeo to see her naked because she has scars on her legs.
Chapter 41: Juliet has a self-harm relapse in which she cuts her legs multiple times. She has a brief moment of suicidal ideation where she considers if she wants to die. This is the only chapter in the book that has on-page self harm and is descriptive. You can skip this chapter, just know that Juliet manages to get home and is very upset after what happened at the bakery.
Chapter 42: Romeo finds Juliet after she has cut herself. Descriptions of blood and her injuries. Romeo cuts his own chest out of a desire to take Juliet’s pain. He tends to her wounds.
Chapter 45: Romeo gives Juliet a list of coping skills for self-harm. They discuss what happened the day before.
Chapter 60: Juliet has the brief urge to cut.
Chapter 70: Juliet has the urge to cut and imagines what it would look like if she did.
Various scenes: Romeo kisses Juliet’s scars.