How does hot air act in zero gravity? In an environment with gravity, hot air is less dense than cool air, so it rises.
How does hot air interact with cold air in a zero gravity environment, in terms of movement? Does it just stay where it is? Some sort of spherical configuration, maybe with the hotter air on the outside?
For the sake of an example, imagine there's a candle burning in zero-g. I'm aware the flame will be spherical. How will the hot air around the flame act?
I found this Reddit discussion on the topic, but being Reddit there's not really a definitive answer like the kind I expect to see here.
 A: In the presence of a gravitational field the hot air raises because it feels a buoyancy force. There is a difference of pressure between the bottom and the top of the hot air portion resulting in an upward force.
If there is no gravity, there is no difference of pressure (in principle) so the hot air does not raise. It just expands uniformly. If you are in an accelerating frame though you get a pressure gradient and the hot air will follow this direction even though there is no gravity.
A: In addition to diffusion, you will see thermal conduction.  Hot gas simply has more kinetic energy, so they move faster.  The hot/fast molecules will travel in various directions away from the heat source and collide with the slower/colder molecules.  Upon collision, there will be a transfer of momentum. Eventually everything will mix up to a thermal equilibrium. The following animations illustrate both diffusion and thermal conduction:


*

*Video showing hot/cold gas mixing (watch first 15 seconds):  
https://www.youtube.com/watch?v=tEFHkcx2cz0

*Video (45 sec) nicely demonstrates energy transfer of the collisions.    
https://www.youtube.com/watch?v=CXZWRkJeKq0
Note: Molecules in this video are represented from slowest/coolest as blue/yellow to fastest/hottest as orange/red. At first, all molecules are blue/yellow.  The right side of the container is a hot plate. As molecules touch the hot plate, they gain kinetic energy.  All molecules are eventually converted into higher-energy/faster/hoter as denoted by orange/red.
A: As you points very well, in the lack of gravity there is no hydrostatical separation. I.e. it doesn't matter that the warmer air has a smaller density, there is no gravity which would separate them.
But, there are many other effects which would still work, because they aren't caused by the gravity. Most important is the diffusion:

Further, in the case of a lighting candle, not only the temperature will differ, but also the material composition around the light and further off. The burning candle converts the oxygene of the air to carbon dioxide and steam. The diffusion will mix them.
The result is that the candle still has enough oxygen to light, but much fewer:

A: What I can conclude is that in absence of gravity there is no buoyant force so no movement is possible physically but however hot air will start exchanging heat with the cooler air by means of conduction and radiation if they are in contact with each other and only by pure radiation if they are not in contact. ( no convection can takes place because of the absence of gravity) the time required to be in equilibrium can be calculated if mass of gases , volume, and the temperature are known .
A: Im not sure i agree entirely. Where there is air and temperature differences there is movement. Im not sure what an air current does in absence of gravity What shape it takes or how  that shape changes with movement snd direction but i think the equal sphere of heat or pressure could only happen in s motionless lifeless controlled situation. I think the currents and motion of warm and cold wiuld cause places in the sphere to spill outwardly or get pushed away in streams or collapse or cool and cause a build up or back up which will puddle until it  reaches s temperature or current change  so it would move more like s lava lamp  whatever it does without gravity but a tiny current could cause all kinds of reactions. Where warm and cold meet there are swirling eddies not just expansion. What is the sperical equivalent to a collum of rising hot air? A rolling mushroom or a torus like rolling a rubber band or o-ring along a cylinder?
