I have a requirement of Active/Active clustering to be implemented using SQL Server 2012 Standard Edition in shared storage SAN.
This is completely possible. In windows clustering, it's a shared nothing philosophy so this will require at minimum two separate instances.
How the data share or synchronization between the two instances on the the disks of nodes in shared storage is going to achieve on the same.
Per the previous statement I made, this is not possible as Windows Clustering is a shared nothing approach. Thus you cannot use the same disks for multiple resources. In this case, having two separate instances of SQL Server would violate that constraint.
Now, should you want multiple active and converged instances of SQL Server running on different servers, you could look into using peer-to-peer replication. It's not cluster aware but there is nothing stopping you from putting it on top of a clustered instance... it just wouldn't make much sense in my honest opinion.
My concern here is how the data synchronization happens between the two nodes in SQL Server 2012 Standard Edition and how to configure the same?
If you want this to happen, and it must be in a cluster, like Cody said above me, you'll need to use Availability Groups. This, however, it not a multi-master model like Peer-To-Peer replication and thus you would only have a single node available to take write requests - though you could potentially have multiple other nodes server read requests.