Instructions
Look at the face first. If you see the word 'Quartz', then the clock is purely electronic. Some electrically impulsed clocks incorporate the power source into their names, for example the Smiths Sectric wall-clock.
Inspect the back of the clock for any pieces made out of plastic. The backs of clockwork timepieces are usually wooden or metal, while Quartz clocks mostly have plastic backs.
Check the back for a battery compartment, circuitry or any kind of wiring. A clockwork timepiece will not have any of these.