set reply-initial-display

SET REPLY-INITIAL-DISPLAY NO/yes  -  whether to show full reply with REPLY

With the usual NO setting, when you REPLY to a message, you are just 
  prompted to input your message, and you see only what you type in.

If you change it to YES, when you REPLY, you will see all the header fields
  generated (from, to, subject...), and the included original message (if
  you used the "including" option), and then the prompt for your message at 
  the end.  
  
For more help, type "help" and one of the following:
(at any prompt:)  save-init   set   show
(at the MM> or Read> prompts:)  reply