Hello and Welcome!
Every judge has a different set of questions they will ask, and most of the questions depend on the project, too. Have you checked the web site for your science fair to see if they have a "judges" section? There may be sample questions there. For my local fair in Santa Cruz County, the following guide is available (questions are near the end.) http://science.santacruz.k12.ca.us/pdfs/ScienceFairJudgesGuide.pdf
Here are some of the questions from the guide:
○ How did you come up with the idea for this project?
○ What did you learn from your background search?
○ How long did it take you to build the apparatus?
○ How did you build the apparatus?
○ How much time did it take to run the experiments (grow the plants,
○ How many times did you run the experiment with each
○ How many experimental runs does each data point on the chart
○ Did you take all data (run the experiment) under the same
○ How does your apparatus (equipment, instrument) work?
○ What do you mean by (terminology or jargon used by the student)?
○ Do you think there is an application in industry for this knowledge
○ Were there any books that helped you do your analysis (building
○ When did you start this project? How much of the work did you do
○ What is the next experiment to do in continuing this study?
○ Are there any areas that we have not covered which you feel are
I hope this helps!