You can create new SKUs directly in the Edit Product Group view. The new SKU will take on the same group attributes- like Title, categorization, and whatever other attributes are shared across the product group.
Go to the Edit Product Group view for the product group for which you want to add a new SKU (3 vertical dots above the image).
Select ADD NEW PRODUCT.
Enter the SKU value for the new SKU, select ADD.
You can edit the pivot attribute value for the new SKU from this view.
Select SAVE to save your changes.
To edit this new SKU you can reopen the edit product group view and click on the new SKU. This will open up a new window with SKU where you can edit the price, list the SKU, or perform any other actions you might want to do.