One of the many reasons I wish my Grandfather had lived longer (he passed away of a heart attack when I was still a toddler, I barely remember him) was that he was a groundcrewman with the 4th Fighter Group during the war. Looking into his service and reading his old (original printings) of
Mr. Tettleys Tenants and
1,000 Destroyed were what really got me interested in WWII aviation. I'd always thought those old planes were cool, but learning about my connection to them got me hooked.
He originally enlisted in 1942, straight out of High School (turned down a college basketball scolarship according to my relatives who remember that far back) and into the USAAF. Wanted to be a gunner on a B-17, but they took one look at him (at 6'5" and 170 pounds!) and told him he was too tall to fly and sent him to supply. Ended up at Debden until 1946, where he met my grandmother (who grew up in Cambridge) and convinced her that the weather was much nicer in New York and she should come home with him.

My great uncle (grandmothers younger brother, retired Sgt. Maj. in the British Army) remembers when he first met him in about 1943- says he was the tallest and skinniest man he had ever met, and that he already had a full head of grey hair. Also said he was one of the nicest people he ever knew in his life, and that he still mourns him to this day.
My grandmother doesn't talk about the war or my grandfather much (basically only when shes been drinking, and then she gets very depressed), but I've managed to worm out of her that she and her family were very nearly killed twice during the Battle of Britain (an incendiary landed in her backyard in July, missing the house by feet, and the family drove through a Stuka attack on the coast in August. She still can't stand the sound of Stuka sirens when they're on TV.), that she to this day hates Germans (she cried when the Berlin Wall came down, but not for the good reasons), and a few times she's talked about the pilots she remembers from the war. She met several of the pilots of the 4th over the years dating my grandfather (and growing up in the nearest large town to the base) and she remembers Don Blakeslee as a "handsome, arrogant devil" (meant in a good way), Gentile as a "cocky young sod" and Kid Hofer as "as reckless as they came". But she still says none of them could compare to the RAF fighter pilots, of course. But whenever she gets angry or upset at something going on in America, she remembers all the young men who went to England to help them, and she feels better about being here. Sounds sappy, but shes said it many times over the years.
To be honest, I don't know what I'd ask a pilot if I had the chance to sit down and talk to one. Theres so much that they went through that needs to be remembered that I wouldn't know where to start.
But I know I'd love to talk to, in no particular order- a P-38 ace, a 109 ace, and/or a surviving pilot from the 4th. Failing that, I'd take anything I could get and be forever grateful for the opportunity.