How can i get the PO no?

how can i get the PO no?

Hello @Denmark_Del_Puso,
please try this
Syntax:cur_frm.set_value(“source_fieldname”,cur_frm.docname )
for e.g:cur_frm.set_value(“order_acceptance”,cur_frm.docname )
for more details:
http://frappe.github.io/erpnext/user/manual/en/customize-erpnext/custom-scripts/custom-script-examples/

Thanks