It depends on the dock. If your dock allows a 3.5mm audio cable connection (sometimes labeled "auxiliary or “aux”), you can use almost any sound outputting device. You just need a 3.5mm cable, which you can find in any store that carries minor electronics.
Example of 3.5mm cable:
If the dock doesn’t have that output, you’ll might be able to find an adapter of sorts to work with the dock. (Try searching for “3.5mm adapter for ipod dock”.)
