OK, we all know that when you eat corn, it doesn’t seem to get digested a lot. As you can tell from its end product. a-hem
So, how much nutrition does the body actually extract from corn?
Well, given that there are corn flakes, corn meal, hominy grits, and all sorts of other perfectly wonderful examples of corn that we eat that have nutritional value (easy to look up), I’d have to say we extract plenty. 
But I think you mean, if you eat a kernel of whole corn, what happens to it? The answer, I expect, is that it is only the shell that you see excreted, and that how much of the interior gets processed depends upon how well you have masticated your food, how long it stayed in the digestive system, and what else was in there with it while you were digesting it. In short, no simple answer.
I’ve never really, ahem, studied it in detail, but I think it’s only really the tough outer coating of the corn kernel that can pass through untouched, as DS says. The good stuff inside gets digested fine.
Next order of business, carrots in vomit.