Learn Hardcore Korean: naega mannan chingu eolguri gieoknayo? - Do you remember the face of the friend I met?

만난 is the pre-nominal modifier form of the verb 만나다 (to meet). Attaching -ㄴ/은 turns the verb into an adjective that describes 친구. So 내가 만난 친구 literally means “the friend that I met.”

Why is there no 의 between 친구 and 얼굴 (as in 친구의 얼굴)?

In Korean, the possessive marker 의 is often dropped when the relationship is obvious—especially for body parts. Both 친구 얼굴 and 친구의 얼굴 are correct, but the shorter 친구 얼굴 sounds more natural in everyday speech.

Why is 얼굴 marked with the subject particle -이 instead of the object particle -을?

Because the verb here is 기억나다 (“to come to mind”)—an intransitive verb. The thing that “comes to mind” is its subject, so you use the subject particle -이/가. If you used 기억하다 (“to remember”), you would mark 얼굴 with -을 as its object.

What’s the difference between 기억나다 and 기억하다, and why do we use 기억나요 here?

기억하다 = “to remember” (active, transitive; you remember something).
기억나다 = “to come to mind” or “to be remembered” (intransitive; something rushes into your memory).
In this sentence, we’re asking if the face “comes to mind,” so we use 기억나다 → 기억나요?

What does the ending -나요? in 기억나요? express?

The -나요? ending is a polite, curious question form. It’s softer than -습니까? and slightly more formal than casual speech but still warm and conversational—like asking “Do you happen to remember…?”

Why is 내가 used instead of 제가, and could it be omitted?

내가 is the informal first-person subject (“I”).
제가 is the polite form.
You choose one based on your speech level. You can omit 내가/제가 entirely if context makes “I” clear, but including it emphasizes “the friend that I met.”

How could you rephrase this sentence more casually or more politely?

Casual:

내가 만난 친구 얼굴 기억나?
Polite (standard):
내가 만난 친구 얼굴이 기억나요?
More polite/formal:
제가 만난 친구 얼굴 기억하세요?
제가 만난 친구 얼굴이 기억하십니까?

Could you use 생각나다 instead of 기억나다 here?

Yes. 생각나다 means “to come to mind” too.

내가 만난 친구 얼굴이 생각나요?
This sounds almost identical in meaning: “Do you recall the face of the friend I met?”