I heard my sister knocking at my door in Korean 🇰🇷

Sentence info.

Breakdown of the sentence:
• 언니가 (eonni-ga)
  – 언니 means “older sister” (used by a female speaker); the particle 가 marks the subject.
• 내 문을 (nae mun-eul)
  – 내 means “my” and 문 means “door”; the object particle 을 indicates what the action is related to.
• 연주하는 것을 (yeonjuhaneun geos-eul)
  – 연주하다 means “to perform” or “to play (music)” but note that if you mean “to knock” on the door, a more common verb is 두드리다.
  – The verb is used in its modifier form 연주하는 (performing/playing), which turns the verb into a relative clause modifying the noun 것 (“thing” or “the act”).
  – The object marker 을 is attached after the whole noun phrase.
• 들었습니다 (deureosseumnida)
  – This is the past tense polite form of 듣다, “to hear.”

Tips to remember:
• Subject and object markers (가 for the subject, 을 for the object) are attached immediately after the noun.
• To describe an action as a noun (the act of doing something), attach -는 (for present descriptive form) to the verb and then -것을 to nominalize it.
• When you want to say “I heard [someone] doing [something],” structure it as “[Subject]가 [object] [verb modifier] 것을 들었습니다.”

Alternate ways to say “I heard my sister knocking at my door”:
1. 언니가 내 문을 두드리는 것을 들었습니다.
  Romanized: Eonni-ga nae mun-eul dudeurineun geos-eul deureosseumnida.
2. 내 문을 두드리는 언니의 소리를 들었습니다.
  Romanized: Nae mun-eul dudeurineun eonni-ui sorireul deureosseumnida.
3. 언니가 내 문을 두드리는 소리가 들렸습니다.
  Romanized: Eonni-ga nae mun-eul dudeurineun soriga deullyeosseumnida.

Each alternate sentence replaces 연주하는 with 두드리는, which properly means “knocking.”

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