It is a question that he will come back.

我认为上述句子逻辑不通，视为错句。应改为以下表达：

1. It is a question whether he will come back.

2. Whether he will come back is a question.

3. It is not a question that he will come back.

4. That he will come back is not a question.

以上各句中的whether he will come back 或that he will come back，是主语从句。

【讲解】从逻辑上讲，如果句子的谓语“是个问题”，那么主语从句就应该是带有疑问的内容，不应该是陈述的内容，所以，主语从句用whether引导。如果句子的谓语“不是个问题”，那么主语从句就应该是陈述的内容，不应该是带有疑问的内容，所以，主语从句用that引导。