1.
Even though Russian has no such a thing as article but there still are ways to express the idea of certainty and uncertainty. Here "ли" shifts the meaning of the question dramatically. Indeed "У него ли учебник" implies "is it him who got [---] textbook?" here I've omitted article "the" but the sentence still seems to bear the sense that the question is about a certain specific textbook and article "the" should be placed in the position [---] anyway.

2.
This is another example when translation from one language to another utilize quite different language constructions.
Его сегодня нет дома. - There is no him at home today.
While in Russian it is a typical construction in English such a sentence doesn't look natural. This is why "He" and "Его" plays different roles in the sentences of different languages.