I have seen customers re-name/re-purpose the 'User-Defined' fields on the Purchase Requisition Entry window, in order to use it as a approval step condition or to provide additional information with the requisition, such as making it a comment field.
Via the Requisition Setup window, you can re-name the User-Defined fields to something like 'Comment1' and 'Comment2'.
If you're able to customize the Purchase Requisition Entry window, you could also make these fields required, depending on what you want setup.
Once you have the fields setup for the comments, you could add them to the email notifications sent out to approvers as needed.
The POP10200 table does look to have the USERDEF1 and USERDEF2 columns in it, so most likely that is where the comments would be stored once setup.
Thank you,
