Is it always necessary to include a research question in the introduction of a paper?
If you are writing a research paper it is quite difficult not to have a question in some form. The purpose of the introduction is to set your study (question/gap of knowledge or what have you) in perspective, to narrow the focus down from a slightly bigger picture to the gap you are trying to fill or narrow even further with your study. Even if your paper is a review, you are doing a review for some specific purpose.

So, you may be thinking too narrowly if you think of a question as a sentence with a question mark, the focus of your paper will be your research question, usually a gap in knowledge where you through your study takes our knowledge beyond the current limits.