Here is the Final answer where I'm extracting all the joint coordinates and then publishing them in each topic.

include <ros ros.h="">

include <tf transform_listener.h="">

include <geometry_msgs twist.h="">

int main(int argc, char** argv) { ros::init(argc, argv, "my_skeleton_tf_listener");

ros::NodeHandle node;

// publisher declaration
ros::Publisher neck_joint = node.advertise<geometry_msgs::Point>("neck_joint", 1);
ros::Publisher head_joint = node.advertise<geometry_msgs::Point>("head_joint", 1);
ros::Publisher torso_joint = node.advertise<geometry_msgs::Point>("torso_joint", 1);
ros::Publisher left_shoulder_joint = node.advertise<geometry_msgs::Point>("left_shoulder_joint", 1);
ros::Publisher left_elbow_joint = node.advertise<geometry_msgs::Point>("left_elbow_joint", 1);
ros::Publisher left_hand_joint = node.advertise<geometry_msgs::Point>("left_hand_joint", 1);
ros::Publisher right_shoulder_joint = node.advertise<geometry_msgs::Point>("right_shoulder_joint", 1);
ros::Publisher right_elbow_joint = node.advertise<geometry_msgs::Point>("right_elbow_joint", 1);
ros::Publisher right_hand_joint = node.advertise<geometry_msgs::Point>("right_hand_joint", 1);
ros::Publisher left_hip_joint = node.advertise<geometry_msgs::Point>("left_hip_joint", 1);
ros::Publisher left_knee_joint = node.advertise<geometry_msgs::Point>("left_knee_joint", 1);
ros::Publisher left_foot_joint = node.advertise<geometry_msgs::Point>("left_foot_joint", 1);
ros::Publisher right_hip_joint = node.advertise<geometry_msgs::Point>("right_hip_joint", 1);
ros::Publisher right_knee_joint = node.advertise<geometry_msgs::Point>("right_knee_joint", 1);
ros::Publisher right_foot_joint = node.advertise<geometry_msgs::Point>("right_foot_joint", 1);

// listener 
tf::TransformListener listener;

ros::Rate rate(50.0); // frequency of operation

while (node.ok())
{
    // Transforms declared for each joint
    tf::StampedTransform transform_neck, transform_head, transform_torso, 
                            transform_left_shoulder, transform_left_elbow, transform_left_hand, 
                                transform_right_shoulder, transform_right_elbow, transform_right_hand, 
                                    transform_left_hip, transform_left_knee, transform_left_foot,
                                        transform_right_hip, transform_right_knee, transform_right_foot;
    try
    {
        // each joint frame to reference frame transforms 
        listener.lookupTransform("/neck_1", "/openni_depth_frame",ros::Time(0), transform_neck);
        listener.lookupTransform("/head_1", "/openni_depth_frame",ros::Time(0), transform_head);
        listener.lookupTransform("/torso_1", "/openni_depth_frame",ros::Time(0), transform_torso);
        listener.lookupTransform("/left_shoulder_1", "/openni_depth_frame",ros::Time(0), transform_left_shoulder);
        listener.lookupTransform("/left_elbow_1", "/openni_depth_frame",ros::Time(0), transform_left_elbow);
        listener.lookupTransform("/left_hand_1", "/openni_depth_frame",ros::Time(0), transform_left_hand);
        listener.lookupTransform("/right_shoulder_1", "/openni_depth_frame",ros::Time(0), transform_right_shoulder);
        listener.lookupTransform("/right_elbow_1", "/openni_depth_frame",ros::Time(0), transform_right_elbow);
        listener.lookupTransform("/right_hand_1", "/openni_depth_frame",ros::Time(0), transform_right_hand);
        listener.lookupTransform("/left_hip_1", "/openni_depth_frame",ros::Time(0), transform_left_hip);
        listener.lookupTransform("/left_knee_1", "/openni_depth_frame",ros::Time(0), transform_left_knee);
        listener.lookupTransform("/left_foot_1", "/openni_depth_frame",ros::Time(0), transform_left_foot);
        listener.lookupTransform("/right_hip_1", "/openni_depth_frame",ros::Time(0), transform_right_hip);
        listener.lookupTransform("/right_knee_1", "/openni_depth_frame",ros::Time(0), transform_right_knee);
        listener.lookupTransform("/right_foot_1", "/openni_depth_frame",ros::Time(0), transform_right_foot);

    }
        catch (tf::TransformException &ex) 
    {
        ROS_ERROR("%s",ex.what());
        ros::Duration(0.10).sleep();
        continue;
    }

    // geometry points declaration for storing 3D coordinates of joints and then published later 
    geometry_msgs::Point neck_pose, head_pose, torso_pose, 
                            left_shoulder_pose, left_elbow_pose, left_hand_pose,
                                right_shoulder_pose, right_elbow_pose, right_hand_pose, 
                                    left_hip_pose, left_knee_pose, left_foot_pose, 
                                        right_hip_pose, right_knee_pose, right_foot_pose;

    // joint position extraction and store
    // neck joint                                   
    neck_pose.x = transform_neck.getOrigin().x();
    neck_pose.y = transform_neck.getOrigin().y();
    neck_pose.z = transform_neck.getOrigin().z();
    // head joint
    head_pose.x = transform_head.getOrigin().x();
    head_pose.y = transform_head.getOrigin().y();
    head_pose.z = transform_head.getOrigin().z();
    // torso joint
    torso_pose.x = transform_torso.getOrigin().x();
    torso_pose.y = transform_torso.getOrigin().y();
    torso_pose.z = transform_torso.getOrigin().z();
    // left shoulder joint 
    left_shoulder_pose.x = transform_left_shoulder.getOrigin().x();
    left_shoulder_pose.y = transform_left_shoulder.getOrigin().y();
    left_shoulder_pose.z = transform_left_shoulder.getOrigin().z();
    // left elbow joint
    left_elbow_pose.x = transform_left_elbow.getOrigin().x();
    left_elbow_pose.y = transform_left_elbow.getOrigin().y();
    left_elbow_pose.z = transform_left_elbow.getOrigin().z();
    // left hand joint
    left_hand_pose.x = transform_left_hand.getOrigin().x();
    left_hand_pose.y = transform_left_hand.getOrigin().y();
    left_hand_pose.z = transform_left_hand.getOrigin().z();
    // right shoulder joint
    right_shoulder_pose.x = transform_right_shoulder.getOrigin().x();
    right_shoulder_pose.y = transform_right_shoulder.getOrigin().y();
    right_shoulder_pose.z = transform_right_shoulder.getOrigin().z();
    // right elbow joint
    right_elbow_pose.x = transform_right_elbow.getOrigin().x();
    right_elbow_pose.y = transform_right_elbow.getOrigin().y();
    right_elbow_pose.z = transform_right_elbow.getOrigin().z();
    // right hand joint
    right_hand_pose.x = transform_right_hand.getOrigin().x();
    right_hand_pose.y = transform_right_hand.getOrigin().y();
    right_hand_pose.z = transform_right_hand.getOrigin().z();
    // left hip joint
    left_hip_pose.x = transform_left_hip.getOrigin().x();
    left_hip_pose.y = transform_left_hip.getOrigin().y();
    left_hip_pose.z = transform_left_hip.getOrigin().z();
    // left knee joint
    left_knee_pose.x = transform_left_knee.getOrigin().x();
    left_knee_pose.y = transform_left_knee.getOrigin().y();
    left_knee_pose.z = transform_left_knee.getOrigin().z();
    // left foot joint
    left_foot_pose.x = transform_left_foot.getOrigin().x();
    left_foot_pose.y = transform_left_foot.getOrigin().y();
    left_foot_pose.z = transform_left_foot.getOrigin().z();
    // right hip joint
    right_hip_pose.x = transform_right_hip.getOrigin().x();
    right_hip_pose.y = transform_right_hip.getOrigin().y();
    right_hip_pose.z = transform_right_hip.getOrigin().z();
    // right knee joint
    right_knee_pose.x = transform_right_knee.getOrigin().x();
    right_knee_pose.y = transform_right_knee.getOrigin().y();
    right_knee_pose.z = transform_right_knee.getOrigin().z();
    // right foot joint
    right_foot_pose.x = transform_right_foot.getOrigin().x();
    right_foot_pose.y = transform_right_foot.getOrigin().y();
    right_foot_pose.z = transform_right_foot.getOrigin().z();

    // joint positions publish
    neck_joint.publish(neck_pose);
    head_joint.publish(head_pose);
    torso_joint.publish(torso_pose);
    left_shoulder_joint.publish(left_shoulder_pose);
    left_elbow_joint.publish(left_elbow_pose);
    left_hand_joint.publish(left_hand_pose);
    right_shoulder_joint.publish(right_shoulder_pose);
    right_elbow_joint.publish(right_elbow_pose);
    right_hand_joint.publish(right_hand_pose);
    left_hip_joint.publish(left_hip_pose);
    left_knee_joint.publish(left_knee_pose);
    left_foot_joint.publish(left_foot_pose);
    right_hip_joint.publish(right_hip_pose);
    right_knee_joint.publish(right_knee_pose);
    right_foot_joint.publish(right_foot_pose);

    rate.sleep();
}

return 0;

};

CMakeLists.txt find_package(catkin REQUIRED COMPONENTS std_msgs tf )

add_executable(skelCord src/skelCord.cpp)

target_link_libraries(skelCord ${catkin_LIBRARIES})

here skelCord is the .cpp file.

if anyone finds any error or has any doubt then please let me know.

Regards, Prasanna