There is no need to find the key code, because FBReader will do that for you under the Keys tab (hit the key in the "action for key" row).
Desktop FBReader does typically require customization, see Visual Tour of FBReader on a Pepper Pad 3
, which is somewhat out of date, or just browse the tabs under Preferences. The non-default actions I like are "Goto Next (Previous) TOC Section". This allows you to skip stories in short story collections for example. The Kindle 2 now has something similar with waypoints, but in FBReader you get them automatically providing FBReader detects (or builds) a TOC. If you include a progress bar with section marks, this jumps to the next/previous mark.