Finding Windows 10 Universal font icons and viewing them visually can be difficult to locate. This page provides a list of fonts (and their symbols) and guidelines for using the Segoe MDL2 icons for Windows 10 Store Apps.
Styles/FontSizes.xaml entry might look something like -
C# example code I am using with a Navigation Pane -
If you work mostly offline (like I do), you can always pull up Windows Character map and select Segoe MDL2 Assets -
See that U+E001 value? That translates to -
FontIcon = "\ue001"