The volume icon appears in Windows 8 notification area -- otherwise known as the system tray -- by default, but it may have been turned off or concealed. If it's simply hidden, clicking the small triangle in the notification area opens a box that displays hidden icons. However, to avoid the extra step, turn on the volume controls and choose to always display the icon.
Turn the Volume Icon Back on
If the Volume icon has been turned off, it won't appear in the notification area, the hidden icon panel or the Notifications Area Icons configuration screen. To turn it back on, right-click an empty area of the Windows taskbar, select "Properties" and then click "Customize" in the Notification Area section. Click "Turn System Icons on or off" and then select "On" next to the Volume entry. Alternatively, click "Restore Default Icon Behaviors" from the System Icon screen to return Windows 8's defaults. The Volume icon should immediately be enabled, but it could still be hidden from view. Click "OK" to return to the Notification Area Icons screen.
Make the Volume Icon Visible
Click the "Volume" drop-down menu in the Notification Area Icons screen and then select "Show Icons and Notifications" to make it visible again. The other options are "Only Show Notifications" and "Hide Icons and Notifications," both of which move the Volume icon to the hidden icon panel. Alternatively, select "Always Show All Icons and Notifications on the Taskbar" to display all icons, including the volume icon if it's been turned on. Click "OK" to exit the screen.