Learn Hardcore Korean: naeil chingureul mannalji moreugesseoyo. - I don’t know if I’ll meet a friend tomorrow.

The pattern -ㄹ지 모르겠다 (polite form -ㄹ지 모르겠어요) expresses uncertainty about a future action or situation. Literally it’s “I don’t know whether (something will happen).” In 내일 친구를 만날지 모르겠어요, it means “I’m not sure if I’ll meet my friend tomorrow.”

Why is 만날지 used instead of just 만나다?

To attach -ㄹ지 모르다, you need the verb stem plus -ㄹ지. For 만나다 (to meet):

Drop -다 → 만나
Add -ㄹ지 → 만날지
This -ㄹ지 creates the “whether or not” clause.

Why does 친구 take the object particle -를 here?

만나다 is a transitive verb, so its object (the person you meet) must be marked. 친구 is that object, so you add -를 → 친구를 만날지 모르겠어요.

What’s the difference between 몰라요 and 모르겠어요?

몰라요 is the plain present form “I don’t know.”
모르겠어요 uses the suffix -겠-, adding a nuance of conjecture or tentativeness: “I’m not sure” or “I guess I don’t know.” It softens the statement and is often used with -ㄹ지 to highlight uncertainty.

Which politeness level does the ending -어요 represent?

The -어요 ending is the polite informal (haeyo) style. It’s respectful enough for strangers and acquaintances but not as formal as -습니다 style.

Can I say 친구를 내일 만날지 모르겠어요 instead of 내일 친구를 만날지 모르겠어요?

Yes. Korean word order is relatively flexible. Both sentences mean the same thing. Placing 내일 at the front emphasizes “tomorrow,” but either order is grammatically correct.

How is 내일 친구를 만날지 모르겠어요 different from 내일 친구를 만날 수도 있어요?

-ㄹ지 모르다 (만날지 모르겠어요): Emphasizes your uncertainty or lack of knowledge about whether the meeting will happen.
-ㄹ 수도 있다 (만날 수도 있어요): States that it’s possible or there’s a chance the meeting might happen.
The first focuses on “I don’t know,” the second on “it could happen.”