How to display comment meta under each comment content

You will need get_comment_meta to pull that information from the database. You will need to know the metakey. If you don’t have that, you will have to search the theme/plugin that generates the metadata for the occurence of add_comment_meta to find it.

Where to hook depends on how your theme is listing the comments. If it simply uses wp_list_comments there is no filter to simply attach the metadata. You will need to change the callback argument using the wp_list_comments_args filter. Then you can make a callback function that specifies which comment and meta data to display and how (learn more).