In invoice name field holds the customer reference. so you can use [[ o.name ]] to get the customer reference

You can not directly get client_order_ref, it is sale order field.

def _get_client_order_ref(self, data):

    ref = ''
    sale_obj = self.pool.get('sale.order')
    sale_ids = sale_obj.search(cr, uid, [('origin', '=', data.origin)]
    if sale_ids:
        ref = sale_obj.browse(cr, uid, sale_ids[0]).client_order_ref
    return ref

you have to do something like this