The even numbered panels in the Menin Gate are on your left, the uneven on your right when facing the centre of Ieper (i.o.w. with your back towards the canal). You will find this panel by entering the gate in the middle of the memorial on your right, the stairs up right or left where you will see the gallery as in below picture.

In total are 8 VC holders mentioned on the Menin Gate Memorial panels.

Enter the gallery via the left door , panel 35 is immediately on your left where the door is and Vallentin is mentioned above the door.