How to get data in table?

ill try to get single field in table for my print format but it doesnt work.

the result print would be NONE?

{{frappe.db.get_value(“Purchase Invoice Item”, “Expense Head”, “expense_account”)}}

You should be doing:
frappe.db.get_value(doctype, docname, fieldname)

I’m sure the docname for your Purchase Invoice Item cannot be “Expense Head”