what would you say

  1. What would you say about it?
  2. What would you say on it?
  3. What would you say for it?

Please let me know which prepositions are correct. Thanks

The first is the most usual/common.

You can use ‘on’ with the meaning of ‘what would you say on the subject of …’ (regarding this subject).

‘For’ could only really be used if you were being asked to debate ‘for’ or ‘against’ a subject.

“Are you going to say for it or against it?”
Is this sentence correct?

Not using ‘say’ but if you change ‘say’ to ‘argue’ then it would be.