Just check the official AcceptDialog documentation:
https://docs.godotengine.org/en/stable/classes/class_acceptdialog.html
then you can go down through base classes to check what other signals you can use.
AcceptDialog defines only confirmed signal but as a subclass of CanvasItem it also offers hide.
As for connecting show it was just for leaving dialog visible all the time.
Replace the code in test project with this one to see how confirmed and hide are emitted.
# Test.gd
extends Control
func _ready() -> void:
$AcceptDialog.connect("confirmed", self, "on_confirm")
$AcceptDialog.connect("hide", $AcceptDialog, "show")
$AcceptDialog.connect("hide", self, "on_hide")
$AcceptDialog.show()
func on_hide() -> void:
print("hide")
func on_confirm() -> void:
print("confirm")