PhD position interview: How specific should my idea of the topic be?
The way I interpret the topic you were asked to present on is that they want you to present on some work you have complete such as your first paper (or possibly a masters thesis if you have not published anything).

The idea of this is probably to get an idea of how you think/do research and provide a nice introduction into finding out what your interested in.

From your question it sounds like you think they are asking for something else. Now I could be entirely misunderstanding what is asked for (I just have your question), but if you are unsure I would suggest you send a polite email to clarify what the talk should cover.

For what you should say in the talk I would try and answer these questions:


What was the motivation for the research (why is it interesting)?
What did you do?
What are your results/what do they show?
Why are the results significant/interesting?