Her mother knocked on the door.

Source: Tatoeba

You are always to knock before entering my room.

You are always to knock before you come into my room.

Source: Tatoeba

Please do not enter the room without knocking.

Source: Tatoeba

Someone's knocking at the door.

Source: Tatoeba

He was roused by a loud knocking at the door.

Source: Tatoeba

Who's knocking on the door?

Source: Tatoeba

I heard a knock at the door.

Source: Tatoeba