"Tell me why he is crying?" Does the sentence end with a period or a question mark?

That depends on the context in which this sentence is put. If you put it in the context of expressing a sentence, it simply means that he is crying, you can use a period. If you put it in the context of doubt, you are confused. If you say why you are crying, you can use a question mark. This is the different meaning of the same sentence in different contexts, which needs specific analysis.