Which is the Postgres version

Simply check the version by this command: psql --version

To determine the version of the database server, use select version() (from a connection to the database):

postgres=# select version();
                                                version                                                     
----------------------------------------------------------------------------------------------------------------
 PostgreSQL 9.2.14 on x86_64-unknown-linux-gnu, compiled by gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-16), 64-bit

To determine the version of the database client, use psql --version (from your shell command line):

$ psql --version
psql (PostgreSQL) 9.6.2

The server is where data is stored. The client is the software you use to connect to the server. They can be different versions.