A.T. Robertson Commentary John 6:28

"They said therefore unto him, What must we do, that we may work the works of God?" — John 6:28 (ASV)

What must we do? (Τ ποιωμεν; ). Present active deliberative subjunctive of ποιεω, "What are we to do as a habit?" For the aorist subjunctive (ποιησωμεν) in a like question for a single act see Lu 3:10. For the present indicative (ποιουμεν) of inquiry concerning actual conduct see Joh 11:47 (what are we doing?).

That we may work the works of God (ινα εργαζωμεθα τα εργα του θεου). Final clause with ινα and the present middle subjunctive, "that we may go on working the works of God." There may have been an element of vague sincerity in this question in spite of their supercilious attitude.