Rap somebody on/over the knuckles
Definition 1 of 1
Pro Tip 1/3Metaphorical Use
It's metaphorical, not literal. No physical action is involved, just verbal or written criticism or correction. 
The manager rapped him on the knuckles for his report's mistakes.
Pro Tip 2/3Mild Criticism
The phrase implies a mild or moderate form of correction, rather than a severe punishment. 
She was rapped on the knuckles for forgetting to attach the document.
Pro Tip 3/3Informal Setting
This phrase is often used in informal contexts among friends, family, or coworkers. 
I got rapped over the knuckles for being late to the lunch gathering.