PICO is a mnemonic used to describe the four elements of a good clinical question. It stands for:
P - Patient/Problem/Population
I - Intervention
C - Comparison
O - Outcome
For Diagnosis, you may consider using:
P - Patient
I - Test
C - Standard
O - Outcome
For Prognosis:
P- Patient
F - Factors
O - Outcome (ex. Mortality)
Here are links for more information.