The question wasn't could he do it but why would it be worth doing?

这个句子中的问句属于自由间接引语。试与直接引语和间接引语比较:

1 直接引语：

The question was not "Can he do it?" but "Why will it be worth doing?"

2 间接引语：

The question was not whether he could do it but why it would be worth doing.

3 自由间接引语：

The question was not could he do it but why would it be worth doing?

4 自由直接引语：

The question was not can he do it but why will it be worth doing？

自由间接引语和自由直接引语主要见于文学作品，引述者隐退于后，直接刻画人物的心理活动，使读者能够更接近人物的内心。

在形式上，自由间接引语和普通间接引语一样作时态、人称代词、地点及时间状语的调整，不用引号，保留原来的问句、祈使句或感叹句的句式，感叹句和问句仍然使用感叹号和问号。通常引述分句不出现，或以插入语的形式出现。自由直接引语则保留原话的时态、人称代词、地点和时间状语，但不用引号。引述分句通常省略或以插入语形式出现。

国内非英语专业英语教学不涉及自由间接引语和自由直接引语的内容。具体可参读章振邦《新编高级英语语法》P592-594.