我对这个问题有一些疑问，不太确定。

Wǒ duì zhège wèntí yǒu yīxiē yíwèn, bù tài quèdìng.

I have some doubts about this question, not sure.

他的回答引发了更多的疑问。

Tā de huídá yǐnfāle gèng duō de yíwèn.

His answer raised more questions.

我对他的动机有些疑问。

Wǒ duì tā de dòngjī yǒu xiē yíwèn.

I have some doubts about his motives.