How much excess nutritional energy, in kilojoules, does the adult consume per day?

I believe the answer is 1000 Kilojoules

On average, adults eat about 2300 Calories per day
On average, adults burn about 2000 Calories per day.

So, on average, average adults had excess of nutritional energy of  2300 - 2000 = 300 Cal per day.

If converted to kilojoule, it would be:
300 Cal x 4.184 = 1255.2 kilojoules =1000 KJ

Keep your breathing calm and try to ignore it