What do u know best?

Best would be to choose a subject that can demonstrate to the interviewers your skills, knowledge and advantage over other candidates.

Basically the company has given you a golden chance to prove yourself when they let you choose the topic.
You can talk about your internships, work experience, co-curricular activities, projects etc.

What do you have to impress them?

There is a fine line between self confidence and egoism

I believe what you present should fit into the job description