Answer:
Your answer is static discharge
Step-by-step explanation:
Your negatively charged hand repels electrons in the metal, so the electrons move to the other side of the knocker. ... This allows electrons to suddenly flow from your hand to the knocker. The sudden flow of electrons is static discharge. The discharge of electrons is the spark you see and the shock you feel. I hope this helps, ( the other answer said static electricity which is wrong.) :)