How does one obtain coordinantes from a map that was mapped by turtlebot in Rviz?

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Is there a way to obtain coordinates from a map in Rviz? I tried using the code "rostopic echo /amcl_pose" to fnd its current position but that didnt work. Thats because a certain topic wasnt published but i couldnt find the topic for amcl_pose. How do i solve this? However from what I understand this gives the current position which leads to my followup question;

How do I get positions from a pre-mapped map without the turtlebot being there? Like is there a way to click on a point on the map and get that position?

Thanks for reading.