Where is the candle hottest? Where is the hottest spot above a lit candle? In the flame or just above the flame tip or some cm above the flame or other?
Update
My question more precisely concerns the heat energy I can get from a candle. I can see that isn't necessarily the hottest part. So to make the question more accurate:  
From which part/point of the candle can I get the most heat energy pr. time unit? E.g. if I was to warm something up, which part the candle would then be the most efficient heater?
 A: In the flame.
According to NASA it's the white part.

According to ChemistryViews it's mid-way between wick and edge


... hot reaction Zones II and III ...
  The concentration of OH radicals is highest at the outer edge of the reaction zones, which is why one finds there also the highest temperature, ca. 1400 °C.


I guess these views may not be inconsistent, as the visible edge of the flame may not be at the boundary of the flow of hot or warm gases and particles from combustion (and perhaps entrained/convected air).
A: I believe your question is not, "Which is the hottest part of the candle flame," but rather, "which area around the candle flame produces the most easily captured heat energy?" These are two very different questions.  The goal is to identify the ideal position for energy capture near the flame so that as much energy as possible can be transferred before being converted into either electricity or (more popularly) radiant heat. You obviously cannot insert an energy capture device inside the flame because the process of combustion itself would be interrupted. One popular solution is by the use of a clay pot combined with one or more burning candles placed so that the pot itself becomes a radiant heater.
The overall efficiency of this method can be determined (mostly) by the amount of space separating the pot and the candle since optimal energy capture will require optimal exposure to the flame. The question becomes, "What is the optimal distance between the energy capture device and the flame?  I would suggest that the candle(s) be placed completely inside the clay pot as opposed to outside as is commonly seen in lamp shade configurations with this type of thermal heater. For obvious reasons, such an open air arrangement will achieve less energy capture than will a (nearly) closed system.
If you would like to see my simple design for a thermal candle-flame heater, you can send your request to me at theone1011@mail.com.
