Unable to add Quantity in Stock in Drupal Commerce 8 using Commerce Stock Module I have enabled Commerce Stock Modules and its submodules 
1. Commerce Stock API
2. Commerce Stock Field
3. Commerce Stock Local Storage
4. Commerce Stock UI

Created a Product Type ABC and added a field field_stock(field type Stock Level ) under fields section of Product Type ABC
Under Commerce >>  Configuration >> Stock
I have set the default configuration for STOCK SERVICES as - Use Default - and default value is set to Local Stock


and when I edit the products I see it as 


What am I missing I have added a field but it does not show the text value where I can add quantity for a product ?
You need to configure the Stock Services found at /admin/commerce/config/stock/settings and choose Local Stock for your product variation.

Related topic can be found here.

EDIT: reading your question again and it seems that you added the field to the product itself, instead of adding it to the product variation. Stock field needs to be attached to the stock variation entity.