Diagnosis

As with any nursing diagnosis, you have to fall back on data gathered during assessment and from the chart. I'm going to say that yes, it is possible to "reverse engineer" a medical diagnosis to a nursing diagnosis, the only way to do it is to take that medical diagnosis all the way back to the data from which that diagnosis is made and then use the data to formulate your nursing diagnosis. You cannot directly reverse engineer one from another.

So, knowing what you know of your patient, list all the data points you have and start looking through "the book" to find however many nursing diagnoses are needed for that patient. Nursing Dx or Medical Dx, all driven by the data, and can be the same data. I'm sure that you have more than "make a nursing Dx of wellness NDx or Knowledge Deficit NDx for a 17 y/o with mono..."