The European regulator ESMA has mandated that from 1 November 2017 additional information is supplied on EMIR Trade Reporting messages, and more stringent validation rules are applied to existing information. Where messages do not meet these new standards they will be rejected by the trade repositories.
Notable among the changes is that it is now mandatory to provide a Legal Entity Identifier (LEI) on all trades submitted. An LEI is a unique identifier for a legal entity that may be obtained from one of a number of authorised 3rd party providers (more info on LEIs). There are also changes to handling of package trades (a trade priced as one transaction but made up of multiple trades), new values for the Corporate Sector Code for NFC-s, reporting of IM & VM in collateral reporting, new rules around UTIs, and various other changes across the different asset classes. Full details of changes on ESMA website.
"EMIR II" in this context refers to the amended Regulatory Technical Standards (RTS) 2017/104 and Implementing Technical Standards (ITS) 2017/105 concerning changes to EMIR Trade reporting that was published in Official Journal on 21 January 2017, and live from 1 November 2017. There are other changes to EMIR under discussion within the EC at the moment as a result of the EMIR Review published in May 2017, which are also sometimes referred to as "EMIR II".