Getting a real time position feedback from rviz?

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You don't need to edit the amcl node at all. In the documentation here you can see that the amcl node publishes to a topic called amcl_pose that represents the robot's position with respect to the map origin. All you have to do is open a new terminal and type the following:

rostopic echo /amcl_pose

You can find a tutorial on using rostopic here.

Another option if you're going to be porting the information to a GUI application, you could run amcl while using rosbag, and then view it afterwards with rxbag to view it, export it to .csv files, etc.

EDIT: In order to then return data to the robotino_base node, first look here to see what topics that the node subscribes to. If you want to publish to cmd_vel, you can see that the type is geometry_msgs/Twist (all cmd_vel messages are of this type). So to do this, you must use:

rostopic pub /cmd_vel geometry_msgs/Twist '[1.0,0.0,0.0]' '[0.0,0.0,0.0]'

For more information on how to specify the contents of the message, you can look here. I hope this helps.