What to do if i just wonder how does a doctor assess a knee injury?

Knee pain: They will take a thorough history of your problem 1st. Xrays will likely be taken. A detailed physical exam will be done by the doctor to evaluate your knee. If the problem is clear at this point, treatment recommendations will be given. This can range from exercises or pt, oral or injectable medications, bracing, etc. If further testing is needed, an MRI might be ordered.

By taking a detailed: History, examination, tests like xrays, ct scan/mri. These all are required usually to make a dx.