Question

Who was khocking at the door?

Answer 1

Answer:

the knocking at the door was of Henry, the waiter. When the door opened, he was standing there with a bottle and two glasses

Answer 2

$\implies$ The phrase "knock on the door" usually uses "knock" as a verb. Knocking on a door is using the knuckles of the hand to hit a door to get the attention of someone on the other side of the door. The phrase "knock at the door" uses "knock" as a noun.

Hope it Helps

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