"What is a boy doing?" is a way to ask in Engpsh about what a boy is currently engaged in or occupied with.

The phrase "What is (someone) doing?" is a way to ask about the current activity or occupation of the person in question. It is a common way to inquire about someone's actions or to show interest in what they are currently doing.

Here are some example sentences using this phrase:

"What is the boy doing?"
"I'm not sure, what is he doing?"
"What are you doing?"
"I'm just reading a book, what about you?"

In Chinese, this phrase can be translated as "男生在干嘛?" or "男生正在做什么?"