Honestly, as much as it would pain me to do so, if I were in Schreiber's shoes, I would take the opportunity to try and persuade Der Fuehrer that it would be in the best interests of Germany do do whatever he could to avoid fighting the US directly (use the industrial capacity argument--"we can outfight them, but they can build a dozen ships for every ship we can build, and the same is true of tanks"), and, perhaps, give some thoughts on how the Battle of Britain should be prosecuted ("If I was Churchill, I'd send my bombers to attack some German cities in hopes of angering you into shifting to bombing my cities instead of my factories. If that happens, we shouldn't take the pressure off their industy--it means that they're getting desperate!"). Not necessarily things that would give the game away, but some things that an experienced leader would think of to try and reduce the actual pressure on Germany. Basically, lay out a case that Germany needs to keep the war somewhat limited to be able to win, and to avoid letting the Allies bait us into fighting the fight that they want...
As tempting as punching him in the face would be.
Alternatively, I'd make small talk with him about dogs. One of the few human things about Hitler was how much he loved german shepherds and dobermans; if you can get to discussing them, you can probably keep away from the minefield that is politics and the war, at least until his busy schedule means he has to go on to his next appointment. Hell, he might even take a liking to you if you spend the time talking about canine antics and have a few particularly funny stories of your dog derping...
