"When does he come?"
Translation:Quand vient-il ?
'arriver' means 'to arrive'. As 'to come' and 'to arrive' mean something slightly different in English, so do 'arriver' and 'venir' in French.
Is the t-inversion just for the liaison and pronunciation reasons or does it make "Quand arrive-il" (which could mean "When he comes") into a question?