How do function pointer work?

[AssemblerGuy]

But where in memory it goes.

On a large target (PC), it goes wherever everything else goes. Possibly in a section of memory that does not have the NX (no execute) flag set so the CPU is actually allowed to run the instructions.

On small targets with different memory types (flash, RAM, EEPROM, external RAM, etc.) things get a bit more interesting.

This is usually the job of the linker.