it seems like you are using the wrong connection settings to connect to Oracle, you are using a Postgres JDBC driver instead of an Oracle one:
JDBC Driver org.postgresql.Driver
Make sure you have the Oracle JDBC driver available on your computer, it is not included in the DQGuru download. You'll have to point to the Oracle driver in the JDBC settings of DQGuru.
Then you'll be able to create a connection to connect to Oracle.