This Navajo word approximates to “what(?)” in English. Ha’íí works just as well, especially when speaking quickly, or fluidly.
If you hear or use this in your sentence then it turns that sentence into a question.
Here are a few examples:
Ha’át’íí biniiyé? (For what purpose?)
Ha’át’éegi? (Which part, specifically? Or, Where?)
Ha’át’éego? (In what way?)
Ha’át’íí yinílyé/wolyé? (What is your name?/What is his-her-its name?)
Ha’át’ííshą nínízin? (What do you want?)