I took it to mean SMS, in which case they will be somewhere in the SMS app's data (or maybe in the message database).
To edit and send may depend on the SMS app. The one I normally used saves them to the conversation, so when I re-open that conversation the draft is already there in whatever state I left it. Conversely my phone's built-in app adds drafts to the list of conversations, so you just tap on the the draft message to continue. Yours may be different again.
If you did mean email, then see the post above this. Most clients have a "drafts" folder for each account.