Sarkozy is the flight attendant.
We know that the co-pilot doesn’t live in Davos (2) and that his nearest neighbor is a passenger (4).
That passenger can’t be Mr.Harper, who lives in Davos (1).
From (3) and (4) we know that the co-pilot’s nearest neighbor also can’t be Mr.Obama (because Mr.Obama has $2,000 in his wallet, which is not evenly divisible by 3).
Thus, if the co-pilot’s nearest neighbor is not Mr.Obama and not Mr.Harper, it must be Mr.Sarkozy.
Now, if Mr.Harper lives in Davos (1) and Mr. Sarkozy lives halfway between Cornwall and Davos (as we’ve just deduced), then the third passenger, Mr.Obama, must be the one referred to in (6) and thus lives in Cornwall.
That means, also from (6), that the co-pilot’s name is Obama.
And if Sarkozy is not the pilot (5), then by elimination Sarkozy must be the flight attendant.