The spark plugs on a 2004 Ford Expedition (assuming it has the common 4.6L or 5.4L V8 engine) are located on
the top of the engine, underneath the valve covers. You'll need to remove the valve covers to access them. They're not easily visible or accessible from the top without doing so.
Because of this, you'll need a shop manual or a detailed online guide specific to the 2004 Ford Expedition's engine (4.6L or 5.4L) to see the precise location of each individual plug and the procedure for removal and replacement. A poorly executed removal could damage the engine.
