Fetch data in a selected table row

The problem is in this line of your script:

Code:

$('#ppmpsupplies').on('click', 'tr', edit_item( <?php echo $item->id ?> ));

If you echo a php value in a script section of your page, it is done when the page is outputted by php. This happens only once, so the value of $item->id is the last $item->id php recognizes.
It's better to add a data-id property to each table row (or the button that will trigger AJAX).
Once you start your AJAX action, you can refer to the data-id property of the selected row.