What it the chemical equation for sugar with potassium nitrate?

Oh yes, the good old rocket candy reaction.

The basic idea behind mixing sucrose, or ##C_12H_22O_11##, and potassium nitrate, or ##KNO_3##, is that the sucrose will be oxidized by the potassium nitrate.

In other words, sucrose will be the fuel, and potassium nitrate will provide the oxygen needed for the combustion reaction that takes place.

The balanced chemical equation for this reaction is

##5C_12H_22O_11 + 48KNO_3 -> 24K_2CO_3 + 36CO_2 + 55H_2O + 24N_2##

The products will be potassium carbonate, carbon dioxide, water, and nitrogen gas.

Here's a video that shows a rocket candy experiment