The simplest way to see if your database is part of a data guard setup

Execute this query:

select * from v$dataguard_config;

DB_UNIQUE_NAME	PARENT_DBUN	DEST_ROLE	CURRENT_SCN	CON_ID
proddb01	NONE	PRIMARY DATABASE	238029367683	0
proddb01_stby1	proddb01	PHYSICAL STANDBY	238029353772	0

In this example, I am logged into the database proddb01, the primary database.

The columnn PARENT_DBUN is interesting. It displays "DB_UNIQUE_NAME of the parent database, also known as the database that supplies live redo to the destination."

If executed on the standby database, the output will be reversed, but the principle the same.

Documentation for the view V$DATAGUARD_CONFIG can be found here