Checking Oracle version is quite often task. The simplest method is to login to sqlplus and query V$VERSION view.

sqlplus "/ as sysdba" 

SQL> select * from v$version 

  2  / 



BANNER

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Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 - Production
PL/SQL Release 11.1.0.6.0 - Production
CORE    11.1.0.6.0      Production
TNS for 32-bit Windows: Version 11.1.0.6.0 - Production
NLSRTL Version 11.1.0.6.0 - Production