Q: Is it possible to write a commentary of a research that has not been published?

Thank you for your question. Commentaries are focused articles discussing a particular published manuscript or a development in the field. They assume that the readers are already aware of the topic of the Commentary, and therefore, they should focus of published (or accepted and in-press) work. Unfortunately, one cannot discuss unpublished findings. I would recommend checking the specific guidelines of your target journal to check their recommendations regarding Commentaries.