What is the visa application process for visiting a host country for engineering conference?

Personal interviews varies per case basis. For example, if you're going with business visa or the work visa then you may be asked to visit the office every time. In case of travel or other casual reasons then often interview doesn't take much long and simple verification is required. Each time the case is different depending on your purpose of visit. Business visa have different process and verification compared to other types of visa.

There are instances where just visa application is enough to get it stamped. But those instances differ based on the embassy checklist and the purpose of visit. Most of the time embassy requires facial verification and stamping on your visa. If you're related to government or embassy office or united nations representative then the verification may not be required.

The verification procedure for work visa is dependent on individual cases. As for the specific case of Italy, the applicant is needed to apply for verification at least 15 days prior to the the application.
In your friends' case, the case could be considered as a study cause. He may need to submit the following documents _

1. Clear copy of the graduation certificate. The certificate should clearly mention the university name, applicant's name, year of passing and the registration number.

2. Copy of board examination consisting the same details as above.

3. Marriage certificate ( if applicable) issued by the constitutional authority.

4. Birth certificate issued by the competent authority.

5. Current address proof.

6. Recent photograph.

7. Latest bank statement indicating account number, bank name and branch.

It being a work or study visa, such verification will be undertaken each time you have to apply for Visa.