Mind you...this info applies for J and F ONLY...and I cannot claim absolute certainty (I enjoyed the flat beds so much I slept nearly the whole flight).

There appeared to be a standard AC power outlet in the seat (in what struck me as a really inconvenient location). IIRC, it appeared to be the kind that could accept US 2-prong plugs or European 2-prong plugs. I obviously didn't try it, but that's what it looked like to me. No clue on 110V vs 220V, but most laptop power supplies will accept both these days.

If my recollection is correct, the worst that your friend will need is a plug adaptor (in case I was mistaken about the outlet's ability to accept a US plug). If he's taking a laptop to Europe, he should already have one of these.