Nondisplaced subarticular fracture at the weight-bearing surface of the medial femoral condyle with marked surrounding intramedullary edema. What is sonk. I had a trauma should I be worried about?

Unlikely SONK. Sonk would have shown up on mri. You have in essence a big "bone bruise" . The natural history is not completely defined but usually resolution without long term problems can be expected. You are the correct age and sex for sonk but that condition is very rare. Keep working on range of motion and follow up with your doctor.
Refer to answer. If you hand substantial trauma could cause fracture. In absence of trauma is due to spontaneous osteo necrosis of the knee. This due to the followings: uncontrolled, diabetes( your fasting sugar needs to less than 90) , rheumatoid arthritis( disease and all inflammatory markers needs to be brought to normal), or thyroid problems( TSH need to be below 2.0). Take also 1000 iu of vitamin d3.