Change path according to your theme. I have considered base as theme package.
You can do using
$_item or $_product
object for printing its core attributes like name, description, weight etc.
1. Product Detail Page (dont say to give in Options or Attributes)
magento\app\design\frontend\base\default\template\catalog\product
open file view.phtml in text editor.
<?php echo $this->escapeHtml($_product->getWeight()) ?>
2. To Display in Check Out Page
magento\app\design\frontend\base\default\template\checkout\cart\item
open file default.phtml
<?php echo $this->escapeHtml($_item->getWeight()) ?>
3. To Display in Invoice also.
magento\app\design\frontend\base\default\template\sales\order\invoice\items\renderer
open file default.phtml
<?php echo $this->escapeHtml($_item->getWeight()) ?>
Cheers.
