Magnetic north pole is defined as the part of Earth where magnetic field lines are originating outwards
So here as per the experimental analysis we know that earth is surrounded by magnetic field lines.
These magnetic field lines are due to several causes but it almost shows same trend as we got it from a bar magnet
If we suspend a bar magnet freely near the surface of Earth then that bar magnet will get affected by the magnetic field lines of Earth
So here North pole of suspended magnet always get attracted towards the south pole of the earth magnetic pole
This experimentally founds that Geographic north pole of Earth is always shown by north pole freely suspended magnet on earth which means Magnetic south pole of Earth is at Geographic north pole
So here opposite to that we must have North pole of Earth magnet which means that Geographic south pole is always Magnetic north pole of earth