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A PointCloud2 is simply a raw memory buffer, to interpret it, you need to use a PointCloud2Iterator which can be found here.

#include <sensor_msgs/msg/point_cloud2.hpp>
#include <sensor_msgs/point_cloud2_iterator.hpp>

void topic_callback(const sensor_msgs::msg::PointCloud2::SharedPtr msg) 
{
  sensor_msgs::PointCloud2Iterator<float> iter_x(*msg, "x");
  sensor_msgs::PointCloud2Iterator<float> iter_y(*msg, "y");
  sensor_msgs::PointCloud2Iterator<float> iter_z(*msg, "z");

  for(size_t i = 0; i < msg->height * msg->width; ++i, ++iter_x, ++iter_y, ++iter_z) {
    std::cout << "coords: " << *iter_x << ", " << *iter_y << ", " << *iter_z << '\n';
  }
}

That being said, printing to console is a terrible way of debugging. I highly recommend you learn to use a debugger.