When building UWP apps you need to have those nice Font Icons from the Segoe MDL 2 font family. I found this sweet little web site that provides a nice cheat sheet for all these icons.
When you are hard coding CommandBar button or Hamburger menu item icons in XAML you can copy and past the actual text of the icon.
If you are using the character code, you can copy the character code number and put it in your code behind.
Check out the cheat sheet here.