digi.me automatically imports comments on your own posts, but not for posts you liked. To view these comments you will need to visit the original post.
Unfortunately, Facebook no longer support importing other people's comments on your posts, however your own comments will still be imported into your library.
On iOS or Android, swipe the post to the left to open the original post. From there you can read all the comments.
On desktop this can be achieved by clicking on the ••• and selecting 'view on source'.