What is Difference between SDN account and Demo Account? How I can identify which one is the SDN account?

SDN provisions account IDs prefixed with tstdrv*... All tstdrv* accounts show up as Demo accounts when viewed in the SuiteCloud Control Center... They (SDN) also sometimes preload test data, so there will be customers and transactions already in the account when you are given access. It's not explicitly documented that tstdrv* accounts are Demo (or developer) accounts though. You can always email SDN to give you a list of all the account IDs they've provisioned for you so far if you need it.