What are the reactants of a burnig candle?

It is the wax or tallow in the candle. Modern candles use wax which is a mixture of high molecular weight hydrocarbons. Tallow is rendered fat from animals (usually beef or lamb).

Uh, since burning a candle is a standard combustion reaction, Carbon and Hydrogen are on the products side, which means Carbon and Hydrogen both must be in the reactant side.

You should find out what type of candle you're burning, because they're made out of different things.
BUT, the equation should look like this:

wax (find it's composition) + O2 (oxygen) ----> CO2 (carbon dioxide) + H2O (water) + heat

By looking at the equation, you should already know that the wax must contain carbon and hydrogen, just find the chemical formula for your special candle. XD

Just so you know, wax is is hydrocarbon and they typically produce what's above in said standard combustion reaction.

In a burning candle three types of products can be formed from the same reactants.
CH4 + O2----->C + 2H2O
2CH4 + 3O2----->2CO + 4H2O
CH4 + 2O2----->CO2 + 2H2O
So you can conclude that the reactant other than oxygen is methane.(although paraffin wax contains many hydrcarbons methane is the chief component, forming a greater composition by mass than the others, therefore its combustion can be taken into account)
Hope its clear!