If you use the schema wizard you'll have the option to let Incorta determine joins. I'm not sure if it has to be defined keys in the source or if the algorithm is more complex ( e.g. using indexes and column names to determine related fields ), but regardless I always check the wizard's work because years of fantasy novels and 80s sword and sorcery movies have taught me that wizards are old and wise, but also somewhat scatterbrained and prone to mis-assumptions often with hilarious consequences.
Incorta uses the metadata available from the JDBC driver and depending on the connector's implementation, it will create joins when using Schema Wizard.
It does create joins for Oracle if the foreign keys are defined in Oracle. However, it does not always create joins for all connectors. Also, it does not try to guess the join based on the matched column names.