It can be used as a noun or a verb. For example:
* He nīnau iā ia. (He asked her.)
* He aha kāu nīnau? (What is your question?)
There are other, less common ways to express "question" depending on the context, such as:
* Kūkala (to inquire, to investigate)
* Hoʻomaopopo (to understand, to comprehend)
* Hōʻike (to show, to explain)
However, nīnau is the most straightforward and common way to express the concept of "question" in Hawaiian.