From FDT Documentation

Default key binding: CMD+O / CTRL+O

Withing the Editor View, invoking Quick Outline will have FDT open a pop up window that allows users to see a list of the methods, imports and attributes of the currently active class.

There is a search field at the top to allow users to filter the pop up display and using the up and down arrows allows users to select a declaration and then hit enter or return to have FDT jump to that declaration.