What is the ruling on flogging an expatriate with forty lashes for placing his hand on the head of a veiled, seventy-year-old woman, under the pretext of seeking her prayers, and being convicted of harassment?

It is absolutely impermissible for a man to touch the head of a non-mahram woman, even if she is old or if there is a barrier. I understand the specification of permissibility for shaking hands implies the impermissibility of touching anything other than her face and hands, even with a barrier and even if there is no fear of temptation. Touching a non-mahram woman has no prescribed حد (fixed punishment) in Islamic law, but the judge may impose a discretionary punishment (ta'zir) for it.