I only find compute pe/atom command. It can compute pair energy, but how can I compute Coulomb energy of per tom?
A direct computation during the run is not possible without significant changes to the source code.
But you can determine is after the fact by recording a trajectory with the full force field, and then use the rerun command — LAMMPS documentation while only defining Coulomb interactions. Then compute pe/atom pair kspace will only contain the Coulomb contributions.
Do you want only Coulomb energy, or Coulomb energy included with everything else?