Hopefully your two layouts refer to two different tables of the same name as data is stored in tables--not layouts, I'll refer to tables, but user your layout names on the assumption that they are the same names.
You need this relationship:
Work Order::WorkOrder# = TimeSheet::WorkOrder#
With this relationship in place, you do not need a Job # field in TimeSheet, you can simply add the Job # field from Work Order to your TimeSheet layout. If you do want to physically copy the data, it can be done by selecting a "looked up value" field option for your Job# field from the matching field in Work Order.