Serial Number is an Inventory Item Valuation Method.  If your Parent Item being manufactured is a Serial Valuation Method, you associate the serial number when putting the parent item into inventory.  If your component items area also Serial Number Valuation, then when you Issue them to the Production Entry, you specify what existing serialized component was pulled from inventory to manufacture the parent item. 

If you want to know exactly what "component serial number" is associated to the specific parent serial number item, I suggest you do production entries one unit at a time or look for an "add-on enhancement" to assist with knowing what component serial number went to which parent item. 

Do you know where I can find instructions on this?  Thanks!!!  

The Sage 100 Help files are a good place to start:

https://help-sage100.na.sage.com/2022/index.htm#cshid=6100&chm=BM