Certificate

Yes, a commerce student can surely do this course.

Just Java certification without any Computer Science or IT degree will not provide you sufficient skills to get a job. You may please visit your strategy to join IT industry.

Quality Assurance is process oriented and focuses on defect prevention, while quality control is product oriented and focuses on defect identification.
Quality Assurance ensures that the approaches, techniques, methods and processes are designed for the projects are implemented correctly.
Quality assurance activities monitor and verify that the processes used to manage and create the deliverables have been followed and are operative.

You can go through the web development, Android app development, C language or C+ certification courses. It also depends on the computer language you studied in class 12th. If you are looking for the basics then C language will be best one.

Yes, you can. Certificate obtained from NIOS is recognised by DGCA for undergoing CPL training program.

Since you have cleared your Bachelors in engineering it would provide the right basis to build your career in oracle technologies. It would require a lot of effort but if you keep trying, you should be able to do so.