Most cars made after the 1970s have a serpentine belt diagram on a placard mounted under the hood. In vehicles that have had repairs requiring body work, or repainting, it may have been removed or covered during the process.
If the placard is not under the hood a copy of the diagram should be in the owner's manual of the vehicle. The Serpentine Belt Diagrams website has a large collection of belt diagrams, including some for older model cars that did not come with a diagram. Due to the increase in car electrical demands in the 1970s, serpentine belts were introduced to replace multiple V-belts.