What is true is that the field due to the point charge outside of the conductor will not be able to penetrate the shell i.e. there will be no field due to the external point charge anywhere within the conductor nor in the cavity: the field will be **killed off*& by the charges on the outer surface of the conductor. Similarly, the field due to the point charge in the cavity will also vanish for all points exterior to the cavity because it will be **killed off** by the charges on the inner surface of the conductor.
Can you please explain this phenomenon of killing of electric field lines more clearly?
I will be thankful for help!