I have a single pole light in my hall way and want to add a recess light with its own dimmer switch next to the existing light switch
If your wiring is very modern, a neutral wire will be present at the switch box, and adding a new circuit that draws its power at that switch is possible and simple.
If your wiring is not modern enough to have a neutral wire will be present at every switch box, but your circuit is wired with power coming from the service panel to the switch first, then adding a new circuit that draws its power at that switch is possible and simple.
But - if your wiring is not modern, and your circuit is wired with power coming from the service panel to the light first, then there is no neutral path available at the switch, and adding a new circuit is problematical. You will have to draw power for the new circuit from somewhere else.
I don't know how to be completely confident that there is a neutral wire in the switch box, but if there is only one cable entering the box, and the two insulated wires of that cable connect to the two terminals on the switch, then there is no neutral present.
The neutral wire in a switch box usually appears as the white wires from two or more cables connected together, typically with a wire nut. If you have many wire nuts in the box, then the situation is more complex, but one of the wire nuts will be bundle of neutral wires.
Before you modify any electrical wiring, you must know what each existing wire is for and what it is connected to. Do not under any circumstances just start hooking things up to see what works. It is easy to create a circuit that seems to work properly but is in fact a deadly hazard.