In the four regions, I, II, III and IV, the electric fields are described as:
Region I : $E_x = E_0 \sin (kz - \omega t)$
Region II : $E_x = E_0$
Region III : $E_x = E_0 \sin kz$
Region IV : $E_x = E_0 \cos kz$
The displacement current will exist in the region: