Without dielectric : Ceq=C0C0C0+C0=C02 and Qeq=C02×2V0=C0V0
As they are in series so the charge on each capacitors is equal to equivalent charge.i.e
Qeq=q0=C0V0
With dielectric in (I), the capacitance of it becomes kC0
now C′eq=kC0C0kC0+C0=kk+1C0 and
Q′eq=kk+1C0(2V0)=2kk+1q0
Thus the on each capacitor is q′=Q′eq=2kk+1q0=2q01+1/k