The iPhone XS does not support the Apple Pencil.
Apple has just only recently launched a 9.7-inch iPad that comes with stylus support. This is the first non-iPad Pro that works with the Apple Pencil. There have been rumors that Apple is working on a smaller version of the Apple Pencil that will work with an iPhone. It is safe to assume that a future next-generation Max model may include Apple Pencil support. The iPhone XS Max boasts 6.5-inch display, making it almost the size of an iPad mini. If one was to guess, Apple will eventually discontinue the iPad mini in favor of a larger iPhone model with stylus support.