seontaek gwamok jung eoneu gwamogi gajang heungmirowo?

• 선택 과목 means “elective subject(s).”
• 중 (literally “among” or “in the middle of”) marks that you’re choosing from a set.
  So 선택 과목 중 = “among (your) elective subjects.”

• 어느 is used when you’re picking one item from a known set (here, the elective courses).
• 어떤 means “what kind of” and asks for a description or type, not a specific pick.
  Since you’re asking “which one” out of a defined list, 어느 is the correct choice.

No, you can avoid repeating the noun by using 게 (short for 것이). For example:
 • 선택 과목 중 어느 게 가장 흥미로워?
Here 게 stands in for “which course,” keeping it concise.

• 흥미롭다 is a ㅂ-adjective.
• In the present casual form, you drop the final ㅂ and add 워:
   흔히: 흥미롭 + 다 → 흥미롭 + 어 → 흥미로워

• Ending with -어? is the present casual (반말) informal style.
• To make it polite (존댓말), turn 흥미로워? into 흥미로워요? or 흥미롭습니까?
  Examples:
   • 선택 과목 중 어느 과목이 가장 흥미로워요? (standard polite)
   • 선택 과목 중 어느 과목이 가장 흥미롭습니까? (formal written)

• 흥미롭다 = “to be interesting,” focusing on something that piques your curiosity.
• 재미있다 = “to be fun/enjoyable,” emphasizing the enjoyment or amusement factor.
  They’re often interchangeable, but if you want to stress curiosity or intellectual interest, choose 흥미롭다.

가장 is an adverb meaning “most.” In Korean, adverbs directly precede the verb or adjective they modify. Hence:
 가장 + 흥미로워 (not 흥미로워 가장).