Question

The delay line in cro is placed after

Answer 1

It is placed after vertical amplifier to the delay the circuit 

Answer 2

Delay line is placed in the vertical section (i.e) after the Vertical Amplifier in a CRO.

More information on the topic:

In a Cathode Ray Oscilloscope (CRO), the delay line circuit is placed after the Vertical Amplifier. It allows few nanoseconds of time delay in the signal, so that user is able to visualize the leading edge of the wave.