What is the segment and sequence number where the trigger event is found for the outpatient registration?

What is the segment and sequence number where the trigger event is found for the outpatient registration?

1. What is the segment and sequence number where the trigger event is found for the outpatient registration?
2. What is the segment and sequence number where the primary diagnosis is identified?
3. What is the segment and sequence number where the patient gender is found?
4. Give one example where being familiar with the HL7 messages could help you as an HIM professional resolve a computer problem.