Wrist surgery 2 days ago, 1 stitch loose, ~5mm opening. No internal suture, only external chromic dissolvable. Steri-strips suffice? Tensile strength?

See your doc. If you recently had surgery and the surgical wound is coming open, you need to go back to the doc who performed the surgery for additional treatment. You should call them right away and be seen as soon as possible. Infections after orthopedic surgeries can lead to bad outcomes. Don't delay seeing your doc for this!