According to the timetable, the 17:55 flight is the last SK non-stop to CDG. He can connect via CPH, but that flight leaves only 15 minutes later, and gets into CDG 90 minutes later. There is also an AF flight leaving about an hour later.

I agree with jacob_m, it'll be a very tight connection if he has to go all the way to the new F-gates in T5 (about a 10-minute walk + security). But I thought SK still operated flights from the old T5 gates? That would save a few precious minutes.