This is fairly basic GDL.
Asking someone how to do it is akin to asking them to write it for you, because its that simple. I will give you a start.
step 1/ create a new GDL object and set its subtype to "Label"
This takes care of the leader as it is built into the "Label" subtype so you will get all the functionality of the leader in other Labels... pretty cool right.
step 2/ use basic GDL to create the box and text items.
Asking the experts on here to take the time to teach basic GDL will probably not get much response. You need to put the effort in to at least learn the basics on your own.
Creator of Cadswift's parametric GDL libraries
Creator of Infinite Openings and Component Catalogues
Push the envelope & watch it bend
website:
https://cadswift.com.au/
YouTube:
https://www.youtube.com/user/CADSwift/playlists