Thank you, mynick and Hailey! Your answers and examples are always helpful!

건지 is used for emphasis as in "(저녁으로) 밥 먹을 건지 피자 먹을 건지 결정하자"(Let's decide if we eat rice or pizza (for dinner)). It's more emphatic than 밥 먹을지 피자 먹을지 결정하자. 거야 could be used for present tense as in "이렇게 하는 거야"(This is how you do it). You can use 거나 with friends older or younger than you, for example, "이렇게 하는 거나 저렇게 하는 거나 별 차이 없어요(There's no big difference whether you do it this way or that way). Of course you would drop the 요 when talking with younger (and close) friends. Hope this helps. ^ ^

I heard 건지 is used for emphasis, but I'm not entirely sure how to use it and I don't know what it means when I use it. I hardly say 건지 is used for emphasis. It is used to express wonder or uncertainty. As for 거야, is that like です in Japanese (it's kind of just there to end the sentence)? In my book I see that 거야 indicates the future and is really informal. Is this true? Could 거야 be used for present tense or only future? In most cases, 거야 is used in the future tense because it indicates a speaker or a listener’s plan or intention. Please see my above examples. However, it can also express a speaker’s guess and in this case, the tense is present, of course. 아마 늦은 봄이었을 거야. I guess it was late spring. Is 거나 "or"? In my book it says it indicates "or" and can be past, present, or future tense. Yes, you are right. Would I be able to use 거나 with friends that are slightly older than me or should I use them with friends that are younger than me? Because 거나 is merely a connective particle, you can use it with anyone regardless of their age.

I heard 건지 is used for emphasis, but I'm not entirely sure how to use it and I don't know what it means when I use it. I hardly say 건지 is used for emphasis. It is used to express wonder or uncertainty. As for 거야, is that like です in Japanese (it's kind of just there to end the sentence)? In my book I see that 거야 indicates the future and is really informal. Is this true? Could 거야 be used for present tense or only future? In most cases, 거야 is used in the future tense because it indicates a speaker or a listener’s plan or intention. Please see my above examples. However, it can also express a speaker’s guess and in this case, the tense is present, of course. 아마 늦은 봄이었을 거야. I guess it was late spring. Is 거나 "or"? In my book it says it indicates "or" and can be past, present, or future tense. Yes, you are right. Would I be able to use 거나 with friends that are slightly older than me or should I use them with friends that are younger than me? Because 거나 is merely a connective particle, you can use it with anyone regardless of their age.

건지 = 것인지 인지 = 이 (stem of verb "이다) + ㄴ지 ㄴ지 can be used both as question ending particle and a conjunctive ending particle, which express a speaker's vague question. 1) as a question ending particle 무엇을 그린 건지. What did he draw? I wonder what he drew. 2) as a conjunctive ending particle 그녀는 집에 갈 건지 가방을 들었다. I was not sure whether she would come back home but she picked up her bag. 거야 = 것이야 야 is an ending particle that is used both in an interrogate and a declarative sentence. 다 줄 거야? Are you going to give all? 다 줄 거야. I am going to give all. You can distinguish whether it is a question by a speaker's tone. If a speaker raise his tone at the end of a sentence, it is an interrogate sentence. 거나 거나 is a conjunctive ending particle which is used among things to show that either of them can be chosen. 어른 앞에서 술을 마시거나 담배를 피워서는 안된다. You should not drink or smoke before your elders.