From the "Not submitted" page of a request type, a user can choose to select multiple fields with 1 being the minimum. Here are 2 simple scenarios: (I have more scenarios but want to list out 2 right now)
1) If the user selects the 1st mandatory field ONLY, then the system spawn off a ticket and use the [first field workflow] (*this is already done with no problem)
The following is a problem/challenge:
2) If a user selects the 1st mandatory field AND selects the optional field -> the parent ticket will be created with data from the mandatory field using the [first field workflow], a child ticket will be created with data from the optional field using the [optional field workflow]. Once the user hits the "Submit" button, the parent ticket should be able to grab the child ticket ID in its email notification.
The Submit button is only going to create one request. Its first execution step, though, can use the ksc_copy_request command to create the second request with its unique workflow (assuming you are running 7.1 or higher). This command returns the id of the child request and can be stored in a field on the parent.