A clock can hang on a wall, or sit on a desk. Clocks are usually not portable. . Watches are usually small, portable, and worn like jewelry on your wrist.

I clock is usually considered to be anything that can tell time, regardless of it's specific name. In context, a watch is a type of clock that is portable in nature usually worn around the wrist or in your pocket. It tends to be circular.

thank you Peachey

Grammar: "What's the difference between ___ and ___?" (We don't use "of".)