This isn't a very natural English sentence. It would be if there were an object being seen or if it were "Who can see?"
I disagree. "To see" can very well be used intransitively, in which case it usually refers to insight rather than eyesight.
Ah yes that is true but it does not work in this sentence like it would with "Yes I see". I can't imagine anybody using "Who sees?" to find out which person had an insight.
In the example, the question could also be posed to clarify the subject of a prior sentence that used the passive voice. "At that point, [object] is seen." "Yes, but who sees?" Ha, magar kaun dekhta hai?
For English speakers 'Who sees' is not an intuitive translation. And it is happening a lot with the Hindi word to look, looking, seeing, watching.
It is like we have to translate in poor English to get the answer right. Duo, need to to make the corrections faster please.