Who is this.
He pointed to her and asked me who is this?
it has to be WHO is this / this = he or she, when they are there with you in same room or on the street.
He cannot point at them in the Past (was) and say "who is that" , "who was that" <-- this would apply only after a person had walked by in the street, or came into a room and then left/exited. You could say after pointing to the door or in the direction of the person, that has gone by. "who was that". = the person in the past has exited or walked by.
This is called tense agreement, where English is explained with English, and not present/ simple perfect etc. that confuses natives and learners.
He can point at them if they are still present (IS) and towards them if they are no longer present (WAS).