VisualComposer/WPBakery Page Editor: Is any JS event triggered after the Edition pop-in is shown?

Solution: add an action on the tag vc_edit_form_fields_after_render.

    add_action( 'vc_edit_form_fields_after_render', function() {
        echo  '<script src="' . AN_URL . 'test.js"></script>';  // Or something other
    }, 9 );

In the functions.php or equivalent.

(Indeed, the tag vc_edit_form_fields_after_render is used by do_action( 'vc_edit_form_fields_after_render' ) which is located in js_composer\include\classes\editors\class-vc-edit-form-fields.php . So what you type in your add_action callable will be executed after, and only after, the user has opened the Edition pop-in presented in the OP message – this is what I was asking for).