To prove him (πειραζων αυτον). Present active participle of πειραζω, testing him, not here in bad sense of tempting as so often (Matthew 4:1).

What he would do (τ ημελλεν ποιειν). Indirect question with change of tense to imperfect. As in John 2:25 so here John explains why Jesus put the question to Philip.