"You who have such little faith." Jesus addressed Peter this way because Peter became afraid. It can also be translated as an exclamation. Alternate translation: "You have so little faith! Why"
Jesus uses a question to tell Peter than he should not have doubted. You can make explicit what Peter should not have doubted. Alternate translation: "you should not have doubted that I could keep you from sinking." (See: [[rc://en/ta/man/translate/figs-rquestion]] and [[rc://en/ta/man/translate/figs-explicit]])