Asked (επηρωτων). Imperfect tense, repeatedly asked.

What then must we do? (τ ουν ποιησωμεν;). Deliberative aorist subjunctive. More exactly,

What then are we to do, What then shall we do? Same construction in verses Luke 3:12; Luke 3:14. The ουν refers to the severe things already said by John (Luke 3:7-9).