Cortana does not always appear in the Windows 10 taskbar by default. The document provides instructions for pinning Cortana to the taskbar so it is always visible, including right-clicking the taskbar, selecting Cortana, and choosing whether to show Cortana's icon, hide it, or show its search box in the taskbar for quick access.

1. Although Cortana "lives" in your taskbar, she
might not appear there by default. If you don't
feel like opening the Cortana app every time
you need her, pinning her to your taskbar will
save you a little extra time.
How to pin Cortana to your taskbar
on Windows 10

2.  Right-click on the taskbar
 Click on Cortana.

3.  Click on the option you want:
 Hidden: This will hide Cortana from your taskbar.
 Show Cortana icon: This will show Cortana's circle
icon in the taskbar.
 Show Search box: This will enable Cortana's
search bar in your taskbar.