Where is my audit as Oracle sys audit is enable
I know I am late to the party but anyways:

your AUDIT_TRAIL value should be set to DB,EXTENDED and not DB_EXTENDED.

You can change it with:

alter system set audit_trail=db,extended scope=spfile;


Bear in mind that after setting it to DB,EXTENDED you have to restart your instance for changes to take effect.

Find more on very handy Oracle's documentation:

https://docs.oracle.com/cd/B19306_01/server.102/b14237/initparams016.htm#REFRN10006