this is from monitor which start with lighted picture and after second the backlight is stopped.

 

Don't know what you mean by "Push-Pull", but the switching transistors are the ones with the Heat Sink.
I don't think you know anything about that unit - it will be live with High Voltages. My advice - Stay OFF.

 

the question is : which exactly are push pull transistors on that little inverter board?

 

I would say U2 and U3 are mosfet drivers pulsing the Transformers for the backlight.