Best approach to run a simple query against all users
select * from dba_users


You need the DBA role or similar access to select from this table.
In Oracle 12 the columns available are

USERNAME    VARCHAR2
USER_ID NUMBER
PASSWORD    VARCHAR2
ACCOUNT_STATUS  VARCHAR2
LOCK_DATE   DATE
EXPIRY_DATE DATE
DEFAULT_TABLESPACE  VARCHAR2
TEMPORARY_TABLESPACE    VARCHAR2
CREATED DATE
PROFILE VARCHAR2
INITIAL_RSRC_CONSUMER_GROUP VARCHAR2
EXTERNAL_NAME   VARCHAR2
PASSWORD_VERSIONS   VARCHAR2
EDITIONS_ENABLED    VARCHAR2
AUTHENTICATION_TYPE VARCHAR2
PROXY_ONLY_CONNECT  VARCHAR2
COMMON  VARCHAR2
LAST_LOGIN  TIMESTAMP(9) WITH TIME ZONE
ORACLE_MAINTAINED   VARCHAR2