1)You ca enable Sign-On Audit with Maximum Details:
See "Sign-On: Audit Level" profile option --- value "Form Audit". This captures the most detailed information, including user login/logout, responsibility used, and specific forms accessed.
2)It depends.. If you want to audit the apps context (for instance apps user info), then go with the EBS audit.. EBS audit uses database triggers and shadow tables to record historical data about changes to specific tables.. DB audit as you may already know does its job internally. Note that, EBS audit trail does not provide the performance and integrity of the audit records that can be achieved with Oracle Database Auditing.
3)EBS audit may not be able to do that task... I mean you can use EBS Audit option (based on the profile named AuditTrail:Activate) but he captured information primarily reflects "what" (data changes) and "when" (timestamps).
While it might capture the "who" (user responsible) for some actions based on the user associated with the database session, it doesn't directly link data changes to individual front-end user activities.
You may need to go with custom methods (triggers, forms customizations, third party audit tools)
https://docs.oracle.com/cd/E26401_01/doc.122/e22952/T156458T663757.htmSee -> Oracle® E-Business Suite Security Guide