Hi !
Code 39 is the easiest barcode font to be printed in WWI using the FM.
Logic:
You should format your symbol (in WWI Template) in the corresponding barcode font.
The value should have * as prefix and suffix. Your FM should add that value and pass that to WWI. (Instead of looking for abap code, ask your ABAP team to write a FM for this logic based on dummy FM)
When you preview it, you would see in barcode.
Already I explained this in the document, Printing in Bar code in SAP EHS WWI
Regards
Subash Sankar