Use VoiceOver to navigate menus on Mac
The menu bar at the top of the screen contains several menus such as the Apple menu 
If the Trackpad Commander is on, you can use gestures when navigating menus.
Note: VO represents the VoiceOver modifier. See Use the VoiceOver modifier.
Navigate to the menu bar
Press VO-M, or double-tap with two fingers near the top edge of the trackpad.
Navigate in the menu bar
Go to a specific menu: Type the first letter of the menu. For example, type “H” to jump to the Help menu.
Go to the status menus: Press VO-M-M.
Move among the menus in an area of the menu bar: Press VO-Right Arrow or VO-Left Arrow. A sound effect indicates when you’re at the end of an area.
Open Spotlight: Press Command-Space bar.
Use Siri: Press the keyboard shortcut (as specified in Siri & Spotlight settings). If Siri isn’t shown in the menu bar, choose Apple menu
in the sidebar (you may need to scroll down). Go to Menu Bar Only on the right, click the pop-up menu next to Siri, then choose Show in Menu Bar.
If you’re using VoiceOver gestures, drag a finger across the trackpad to navigate the areas and menus in the menu bar. You hear a sound effect when moving over a blank space. You can also flick left or right to move between menus.
Navigate a menu
Open any menu: Press VO-Space bar.
Move down or up a menu: Press VO-Down Arrow or VO-Up Arrow, or drag a finger down or up on the trackpad.
Move to a submenu: Press VO-Right Arrow or flick right on the trackpad. To return to the main menu, press VO-Left Arrow or flick left on the trackpad.
Close a menu
To exit a menu without selecting an item, press Escape, or scrub back and forth with two fingers on the trackpad.
To open a shortcut menu for an item, press VO-Shift-M, or use the customised gesture Control-Trackpad click (you can change this default assignment and assign the command to a different gesture).