USDD contract code is public on tronscan. TRONSCAN | TRON BlockChain Explorer | 波场区块链浏览器
You can deploy you own USDD on testnet with the code. this page includes the most useful link where you can find how to issue an TRC20 token, follow that guide and together with the USDD smartcontract code, you can have your own USDD.
One more info, on that page you can also find the Developers community where you can communicate with other developers, it would be super easy to find answers in the developers groups.