knock at the door
knock on the door

He went with him and knocked on his daughter's door.

The next day he and his daughter knocked on my door.

He would return home later to be available to any who knocked on his door.

I knocked on his door at eight in the morning.

I thought, what would happen if two people knocked on his door?

They knocked on his door to tell him but he didn't answer.

He went to the house and knocked on the door several times.

I knocked on the door and his wife let me in.

He went to her house and knocked on the green door.

One knocked on the door after all were in bed.