How do I reduce kitchen temperature during cooking?
Sucking hot air out of the kitchen using the hood ("chimney") will cool the room, though possibly not by much on a hot day. A nice big open window to allow fresh air in will maximise this effect.  Even on a hot day, the hood will cause a through draught, and the lower humidity, slightly cooler air blowing over you as you cook will be much more comfortable.

In very rare cases where the outside temperature is above the inside temperature (traditional buildings that are designed to cool at night and heat as slowly as possible during the day) there's little you can do.  Such buildings aren't really designed for use with air conditioning (and they often come from a tradition involving outdoor cooking)

Some other things you can do that make at least as much difference:


Cover dishes when cooking and turn the heat down (yes, even if it's not traditional).  This is especially useful when boiling/simmering as the steam contributes to the discomfort.
Some dishes can be brought up to boiling point then insulated to continue cooking.
In a heatwave I've been known to get a long extension lead and an electric hotplate and cook outside (probably not an option in an apartment unles you have a balcony).