How I can set shipping amount for each order items. In my cart, I set for each cart item one shipment but I don't know how I can save it and which model or table saved it?
If you talking about Magento cart items shipping amount for each order items, then take a look on database table
Magento2 does not save each item shipping price at any database table. On the fly means at code level depend on Shipping address/billing address total Shipping rate calculate and it sum save at
quote_shipping_rate and `quote_address.