Enquiries at market sounding usually fall into particular areas.
These are not questions to ask of suppliers, but rather questions that the customer should seek to answer for themselves through dialogue with suppliers.
Points to consider
Maturity: is the market ready to deliver what's required?
Feasibility: will the market be technically capable of meeting the requirement?
Competition: how many suppliers provide what is required; will procurement be sufficiently competitive?
Capacity: are there enough suppliers, with sufficient capacity, to meet the requirement?
Working together: will the requirement bring suppliers from different subsectors together in a new way? How will this work?
Traditions and prevailing attitudes: what are they in this market? How will they affect the project?