[译] 当代的青年人不知道自己想要什么。
[误] The youth of today doesn't know what he wants.

[正] The youth of today don't know what they want.
[注] youth 表示"青年们"，没有单数概念，所以其谓语动词应该用复数，用来指代他们的代词也应该用 they。