You can use Send Mail [ ] script step to send mail with a field as the message body.
If you are on "TAB" table layout at record no 3 and that record has "JobCardNo" field value 123.
In Send Mail  step you can specify the message body field value as "JobCardNo" , which will send the mail with message body as 123.
If you want to add some text along with the Job card number , then this can also be concatenated in the calculations.
Hope this will help.