Have you made a custom module yet? That will need to be your first step if not.

What you will need to do is add a new field to Delivery Orders like so:

'del_loc_rack': fields.related('product_id', 'loc_rack', type='char', string="Rack Location")

Then add that to an .xml file that inherits the Delivery Order view, and place the field 'del_loc_rack'. Hope that helps!