strike a surface noisily to attract attention, especially when waiting to be let in through a door

he strolled over and knocked on a door marked Enquiries

I knocked and waited but no one answered

collide with (someone or something), giving them a hard blow

he deliberately ran against her, knocking her shoulder

he knocked into an elderly man with a walking stick

talk disparagingly about; criticize

approach (a specified age)

he's younger than his brother—knocking seventy