You appear to have two tables with a portal listing information that should be linked by Job ID to the current record in a table that seems to have one record for each job.
I will refer to the layout's table as Jobs and the portal's as JobDetails. Job ID should be defined in Jobs as a number field with an auto-entered serial number. That way, no matter how a new record is created in jobs, each new record get's a new Job ID value and no scripting is required.
Your portal should make use of the following relationship:
Jobs::Job ID = JobDetails::_fkJobID
If you enable "allow creation of records via this relationship" for JobDetails in this relationship, you can add new records in your portal just by entering data into the blank "add" row of this portal. When you create a new record in Jobs, the portal will automatically be empty until you create new records in JobDetails with a matching value in _fkJobID
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained
Thanks again PhilModJunk for your help. I've been using FileMaker Pro for 2 months now and I just realize that I should try this approach using the portals and in the process got stuck. Thank you again for your help and insights.