How can I find that what cargo is loaded on a vessel or ship after or before shipped?

I used to use a shipper to bring in stuff . Seems only your shipping company can provide you with information on where your items are during and after shipping. The manifest would probably be available only to the authorities who want to inspect the goods being shipped.

Are you a pirate?

Include contractual conditions that specify pre-shipment inspection by independent authority.

Finding out what cargo has been shipped after the vessel has sailed is folklorically after the ship has sailed wouldn't you say?

Inspection upon landing prior to payment may also be appropriate.

Contact your government agency responsible for import control.

Do not enter into Irrevocable Letters of Credit unless the exporter is beyond reproach.