maya has tooltips disabled. but you can get the qt menubar and enable it.
note most default maya menu items already have tooltips 

from PySide2 import QtWidgets
main_window = None
for widget in QtWidgets.QApplication.topLevelWidgets():
if type(widget) == QtWidgets.QMainWindow:
main_window = widget
break
print(main_window.findChild(QtWidgets.QMenuBar))
menu_bar = main_window.findChild(QtWidgets.QMenuBar)
# print(menu_bar.children())
for action in menu_bar.actions() :
print(action)
print(action.menu())
action.menu().setToolTipsVisible(True)
you can get the menu-items from your menu and set their tooltip
for action2 in action.menu().actions():
action2.setToolTip("bob")
if you name your maya menu items, action.objectName() will return the name. a good practice to identify your menu items.