Ask if there’s a desire for it in the marketplace (6)
I believe the answer is:
demand
'ask' is the definition.
('demand' can be a synonym of 'ask')
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for demand that I've seen before include "Ask - what the public wants" , "Require; urgent claim" , "Requisition" , "Forceful request" , "Urgent or peremptory request" .)