What kind of track is the Emerald Night set compatible with? According to What different types of lego train tracks exist?, there have been many different kinds of LEGO track. Which kind of track can I purchase that will be compatible with this train?
The set is from the "RC / Power Functions Era", so it's meant to be compatible with those tracks.

Luckily for you those are the only tracks for sale in ordinary stores today.

As the answer to that question says, those tracks have "roughly the same mold" as the 9V track so the train is as compatible with those - I've also seen an Emerald Night set equipped with a 9V motor run on such track.

The gauge of that track is roughly (the profile of the rails is a little different, so depending on how you measure it, there might be a small difference) the same as in the previous eras, so the train can probably also be used on those tracks.

I remember a problem with some parts not moving smoothly through each other when driving backwards, but that is probably independent of the tracks.