Also in Qlik Community https://help.qlik.com/en-US/connectors/Subsystems/ODBC_connector_help/Content/Oracle/Create-Oracle-connection.htm they ask to do something to the tnsnames.ora files ..
*** also one thing i forgot to mention the first time i opened the Oracle SQL Developer for setting up i went to Tools -> Preferences -> Advanced -> there i filled the Tnsnames Directory which was some server path it seems.
I went to the server path which i filled here in oracle SQL Developer (Tools -> Preferences -> Advanced -> there i filled the Tnsnames Directory) and there i saw two files tnsnames.ora and sqlnet.ora, i copied both the files and pasted in the
%USERPROFILE%\AppData\Local\Programs\Common Files\Qlik\Custom Data\QvOdbcConnectorPackage\oracle\lib\network\admin
path as mentioned in the Qlik community and the connection succeded .
Is there any other way using OLEDB or ODBC to connect to the oracle DB ?