The task is to write a comment paper: one that would be suitable for publication in JOST. In your comment paper, you should take issue with ONE aspect of the research paper you are looking at – a flaw which you feel you can show compromises the reliability and robustness of the paper
Your comment paper should identify the flaw, explain why it is a flaw (why it in some way compromises your faith in the findings of the paper), and suggest how the problem could have been avoided and/or could be overcome in future studies of a similar kind.