I would like to know the most possible but I feel like there are questions that I am just not thinking of to ask. Any ideas would be appreciated! Thanks! Here is a link to his WWII pictures http://imgur.com/a/8k3cT
My great-grandfather is 93 and served in the Pacific during WWII from 1942 to 1945. He started off in Australia and then went on to help liberate the islands in the Pacific, mostly The Philippines, and went on to Japan after they surrendered. He saw the aftermath of Hiroshima and also helped guard the body of one of the men who raised the flag at Iwo Jima.
My advice? Leave the big picture stuff alone. Don't ask about generals or campaigns or the kind of stuff you read about in your high school textbook. As a young enlisted man, he probably wasn't privy to the details, and there's a good chance he won't remember that sort of stuff. Asking what he thought about Roosevelt or MacArthur is fine; asking him to analyze their actions (unless he's studied it) or war strategy is probably not going to get you much. Moreover, we do gentlemen like your grandfather a disservice by excessively focusing on that sort of thing. The main thing is to try and get a look at his war, not the war. Regardless of what he did, his experiences are not less important because he didn't have gold braid on his cap brim or rub shoulders with the high and the mighty.
Focus on things that were special to him. How did you feel when you got your draft notice/volunteered? What was basic training like? Who were your buddies? What did you do on leave or during your off hours? Did you like your commanding officer/sergeant? Who was the biggest jerk in the outfit? How did you feel about going overseas? Were there any places that were especially beautiful/poignant? What did you miss most when you were in the Pacific? Things like that. If he still has his campaign ribbons and medals, ask him about them; I knew a 4th Infantry Division veteran who, even as he was being swallowed alive by Alzheimer's, proudly but disjointedly told me how he won the Bronze Star for going toe-to-toe with a German tank with a bazooka at point blank range.
DO NOT ask how many people or how he did it or what the worst thing he ever saw was. A few psychos excepted, no veteran has ever responded well to being asked morbid shit like that. Most will shut down. If he trusts you and wants you to know, he will tell you himself. Try not to bring up things that you know will upset him, like buddies who were killed or mangled; remember that as brave and as noble as he is, he is an old man with seventy years worth of grief weighing on him. Be a little cautious as you feel your way in; when you stumble upon a subject that is too raw, pull back.