While sweet corns are a different variety than the kernels used for popcorn, a workable hypothesis would be that there are enough genetic similarities that drying and popping should work in some form of fashion. In this instance, the claim is that drying the sweet corn kernels, that have sugar inside them naturally, in a similar process to the way that popcorn is dried will produce kernels that are viable for popping.
If you have enough months between now and the science fair, you can buy seeds of sweet corn (sugary, sugary enhanced and supersweet) as well as popcorn and plant several of each in your back yard or some other outdoor green space. All three of these varieties have sugar inside them, so you're testing the ability to grow popcorn with sugar. Buy wooden stakes to secure the plants to as they begin to emerge from the soil. Make sure to water the ground well after you plant the seeds; for most varieties, planting in the spring time is best, so you may need to run this project through the summer and finish the presentation in the fall, saving it for the date of the fair.
Wait until the kernels harden and the husks take on a papery texture. Then, remove the husks. Put the ears on a baking sheet and pre-heat the oven to 300 degrees Fahrenheit. Place the ears in the oven for 20 minutes and then bring the temperature down to the lowest setting. Crack the door open and leave the ears in there overnight. Cut the kernels off with a knife the next day.
Put the kernels into a paper bag, fold the bag closed and place the bag into a microwave oven. Follow the microwave's instructions to see what the experiment will yield.