This case is typical of PCP although due to the marked improvement in treatment of HIV it is far less commonly seen than a few decades ago.
The approach to this chest x-ray in an oral exam where the history of HIV is not given would be to first describe your findings (as detailed above) and then to make statements that show the examiner that you understand how this appearance could represent different pathologies in different clinical settings. You should aim to do this without forcing the examiner to give you any further information. In particular you should avoid asking direct questions of the examiner like "is the patient immunocompromised?" or "is the patient acutely unwell?". Instead you should volunteer each clinical scenario yourself and give your favoured diagnosis based on that.
For example, you might say "If this patient is acutely unwell and known to be HIV positive or at risk of HIV then the appearance would be typical of pneumocystis pneumonia. Alternatively, if this patient is immunocompetent and presenting subacutely then the findings of multiple small cystic spaces, preserved lung volumes and sparing of the lung bases would raise the possibility of pulmonary langerhans cell histiocytosis, which most commonly occurs in smokers."
By following this approach you have given two very good differential diagnoses for the appearance, you've shown off your knowledge and you have done it all without the examiner having to guide you in any way. Remember, an examiner is not there to answer your questions, and when they are forced to say "he had no previous chest x-rays" or "he was HIV positive" you can be fairly certain their voice will sound monotonous to the point somnolence.