В Python нет 2D списков, есть только списки, поэтому вы должны использовать подпись list
.
Пример:
from PySide2 import QtCore
class Sender(QtCore.QObject):
signal = QtCore.Signal(list)
def on_test(self):
l = [["a", "b", "c", "d"], ["A", "B", "C", "D"]]
self.signal.emit(l)
class Receiver(QtCore.QObject):
@QtCore.Slot(list)
def on_receiver(self, l):
print(l)
QtCore.QCoreApplication.quit()
if __name__ == '__main__':
import sys
app = QtCore.QCoreApplication(sys.argv)
sender = Sender()
receiver = Receiver()
sender.signal.connect(receiver.on_receiver)
QtCore.QTimer.singleShot(1000, sender.on_test)
sys.exit(app.exec_())