omit sub summary line items if below a threshhold value?

Summary field values do not refer to a specific record (they refer to a group) and their value changes as the found set changes so that keeps them from being a searchable field.

By defining a field that uses GetSummary to return the same subtotal as your sub summary parts, you could set up a script that uses omit record to loop through your found set and omit all records where this calculation field returns 2 or smaller.

How did you define s_Job_Count getSUBsum?

Omit record moves you to the next record automatically. Try this approach:

If [ JOB::s_Job_Count getSUBsum < 3 ]
    Omit Record
ELSE
    Go to Record/Request/Page [ Previous; Exit after last ]
End If

That should work, but don't see why working from first to last wouldn't also work.

What I hoped, starting the field name with s_, the naming convention for a field of type summary had me concerned.

This script should work for you and only need to be run once:

Sort[Restore; no dialog ] // sort by Title field
Go to record/Request/Page [first]
Loop
   If [ s_Job_Count getSUBsum < 3]
       Omit Record
   Else
      Go to Record/Request/Page [next ; exit after last]
   End If
End Loop