tf broadcaster to subscribe a existing topic

edit

I'm trying to see the point cloud 2 on rviz but because the packages I'm using, the topic camera/points2 does not have a frame ID, so I use the tf_broadcaster to publish a cloud topic that have a frame ID following tf tutorial. Is there any way to make the new topic cloud subscribe to my camera/points2 so that cloud will be the same as camera/points2 and also have a frame ID.

#include <ros/ros.h>
#include <sensor_msgs/PointCloud2.h>

int main(int argc, char** argv){
ros::init(argc,argv,"point_cloud_publisher");
ros::NodeHandle n;
ros::Publisher cloud_pub = n.advertise<sensor_msgs::PointCloud2>("cloud",50);
ros::Rate r(1.0);
while(n.ok()){
sensor_msgs::PointCloud2 cloud;
cloud.header.stamp = ros::Time::now();
cloud.header.frame_id = "sensor_frame";

  cloud_pub.publish(cloud);
 r.sleep();
 }  
 }