SQL Developer will look in the following location in this order for a tnsnames.ora file
To see which one SQL Developer is using, issue the command show tns
in the worksheet
If your tnsnames.ora file is not getting recognized, use the following procedure:
Define an environmental variable called TNS_ADMIN to point to the folder that contains your tnsnames.ora file.
In Windows, this is done by navigating to Control Panel > System > Advanced system settings > Environment Variables...
In Linux, define the TNS_ADMIN variable in the .profile file in your home directory.
Confirm the os is recognizing this environmental variable
From the Windows command line: echo %TNS_ADMIN%
From linux: echo $TNS_ADMIN
Restart SQL Developer