change the contents of the area entered signal from:
func _on_Area2D_player_entered(_player: KinematicBody2D) -> void:
question_box.question_change(level_at)
using = true
pass # Replace with function body.
to:
func _on_Area2D_player_entered(_player: KinematicBody2D) -> void:
_player.get_parent().question_change(level_at)
using = true
Since the node/script that holds the function is on the level node which is the parent of the player that enters the area. That should fix your immediate issue. I have a sneaking suspicion your next problem will be determining what level it is so the correct box gets shown.
Also the pass
keyword is unnecessary if the function is no longer empty.