The fuel filter on a 1999 Dodge Durango is typically a cylindrical canister, usually metal or plastic, with fuel lines connecting to it at either end. It's usually around 4-6 inches long and 2 inches in diameter. It may have a single or double connection, depending on the specific model and engine (it can vary slightly even within the 1999 model year). It will *not* be visually obvious like a large, in-line filter you might find on some other vehicles. It's usually tucked away somewhat, to protect it.
There's no single definitive image since different suppliers might have made slightly different filters over the years, even for the same model vehicle. However, searching online image searches for "1999 Dodge Durango fuel filter" will provide you with numerous pictures that will give you a general idea of what to expect. Paying attention to the engine size in your search will give you even more accurate results.
