You cannot export the content of comments posted on manuals or steps as a list.
However, you can export the number of comments posted on manuals.
*The number of comments posted on steps cannot be exported.
Related: What happens when you add a comment to a manual or step
https://help.teachme.jp/hc/en-us/articles/900005509786
Related: What does each item mean when exporting the manual list as a CSV?
https://help.teachme.jp/hc/en-us/articles/900005507846