Cherished desire? A doctor has it, one needing to get on (8)
I believe the answer is:
ambition
'cherished desire?' is the definition.
'a doctor has it one needing to get on' is the wordplay.
'a doctor has' becomes 'ambi' (I can't justify this - if you can you should give a lot more credence to this answer).
'it' becomes 't' (abbreviation. e.g. in 'tis).
'one' becomes 'i' (Roman numeral).
'needing to get' is a charade indicator (letters next to each other).
'ambi'+'t'+'i'+'on'='AMBITION'
Can you help me to learn more?
(Other definitions for ambition that I've seen before include "Desire to succeed in the world" , "Desire to achieve success" , "Drive to succeed" , "Desire (for riches, fame)" , "Strong desire for success" .)