Can the input of the op amp be 1kV? and can Oscilloscope read such high voltage?
The usual way to get an oscilloscope to deal with 1000V is to use a 100:1 probe. The probe needs a voltage rating above the voltage being measured. A 2kV 100:1 probe is commonplace. It divides the 1000V signal by 100, giving an output of 10V, which most oscilloscopes can handle.

The circuit diagram isn't clear about the amplifier, but my guess is that it is an ordinary low-voltage integrator with the input at a virtual ground. In the intended mode of operation of the circuit, the current ip is low and there is no high-voltage requirement for the integrator.

If the sample is conductive, or if the test cell is otherwise accidentally shorted, you need to decide what should happen. If the integrator is low-voltage, it will be destroyed by 1000V, possibly shattering the IC package and sending little pieces in all directions. After the integrator fails, it might pass the 1000V to the oscilloscope and the opamp power supply, and destroy both of them, also. For this reason, I would use the 100:1 probe to protect the oscilloscope. I would also add MOVs and fuses to the opamp power supplies to absorb any overvoltage from finding its way back into the supply.

To answer your question, the APEX PA89 opamp can handle 1200V. I would design a high-voltage amplifier using discrete components if I needed lower cost. The advantage of using a high-voltage amplifier is that the circuit could be designed to handle a shorted sample.

The buffer amplifier can be a 100:1 resistive divider and then an inverting opamp circuit with a gain of -1.

Here is my boilerplate advice for working with high voltage: High voltages can be lethal. Take all safety precautions. Wear non-conductive shoes. Wear safety glasses. Probe with your left hand in your back pocket. Don't work alone. Make sure someone with you knows CPR. Know where the nearest fire extinguisher is.