In order to do this, we need to create a custom line item field that will get the value of the "On Order" on the Item Record.
Navigate to Customization > List, Record & Field > Transaction Line Fields > New
Label = On Order '
Type = Decimal Number
Store Value = Unchecked
On the Applies to Tab
Sale Item = Checked
On the Sourcing & Filtering Tab
SOURCE LIST = Item
SOURCE FROM = On Order
Hit Save and Apply to Forms
When you create a new sales order, the column "On Order" will display the value sourced from the Item Record. You can customize the form to adjust its location.
Here are instructions on how to do this :
Open a sales order and click con customize > customize form on the top right section of the Sales Order Form
Go to the Sublist Fields Tab
Look for the "On Order" Fields we created and move it the location you like.
Make sure that the Show checkbox is checked for this field.
Save the Form.
This should make the column more visible depending on your needs.