Could refer me to instruction on installing second exchange server 2010 for duplication of DAG.?

Installation is identical as the first server, install pre-requisites, run setup. The configure DAG as per the Technet instructions. Nothing special, other than you must be on Enterprise edition of Windows, and both servers should be the same version (so Windows 2008 or 2008 R2). Simon.Simon Butler, Exchange MVP Blog | Exchange Resources | In the UK? Hire Me.

HI You just need to know DAG Prerequisites. DAG Prerequisites: A DAG has been created. For detailed steps, see Create a Database Availability Group. Because DAGs use WFC technology, all servers added to a DAG must be running either Windows Server 2008 Service Pack 2 (SP2) Enterprise Edition or Windows Server 2008 R2 Enterprise Edition. All servers in a DAG must be running the same operating system. You can't have DAG members that are running Windows Server 2008 SP2 and others that are running Windows Server 2008 R2. You must remove all replicated database copies from the server before you can remove it from a DAG.