First - yes, you did spell interrogative correctly. Secondly, about -까 (gga) ending (Will it be?): ㄹ/을까 (eulgga) is a grammatical structure that usually comes at the end of a sentence. When "ㄹ/을까?" is used when talking about an incident, someone's feelings or the state of things, it expresses a assumptive or suppositive question. Look at the following examples and then I will explain how to use it in a sentence. 내일 은 비 올까요? [The 요 can be removed if you are friendly with the person.] (nae-il bi ol-gga-yo?) Do you think it'll rain tomorrow? The verb 오다 (to come) becomes 오+ㄹ(no 받침)+까요 = 올까요. 승환이 이것을 좋아할까? (seung-hwan-ee ee-goh-seul joh-a-hal-gga?) Do you think Seung-Hwan will like this? The verb 좋아하다 (to like smt/smb) becomes 좋아하+ㄹ(no 받침)+까 = 좋아할까. 언제가 좋을까? (eon-jae-ga joh-eul-gga?) When is a good time (do you think)? The verb 좋다 (to be good) becomes 좋+을(there is a 받침)+까 = 좋을까. Thirdly, as for "니" (ni) at the end of a sentence. This grammatical structure also usually comes at the end of a sentence where it ("니") is added to the base form of the verb. It is used when asking about a current situation, someone's current feelings or the current state of things, most often in an informal way. Look at the following examples and then I will explain how to use it in a sentence. 뭐 하니? (mwo ha-ni?) What are you doing (now)? The verb 하다 (to do) becomes 하+니 = 하니. 내일은 바쁘니? (nae-il-eun ba-bbeu-ni?) Are you busy tomorrow? The verb 바쁘다 (to be busy) becmes 바쁘+니 = 바쁘니. 지숙이 화내니? (gee-soo-gi hwa-nae-ni?) Is Ji-Sook mad at me? The verb 화내다 (to get angry/mad with smt/smb) becomes 화내+니 = 화내니. Finally, when "아" is the ending of a sentence in a question form, it is just the present simple tense without the polite ending "요": e.g. 슈퍼에 가? = "Are you going to the supermarket?". The present tense conjugation has been explained here before I think, so it should be fairly straight-forward.

I just want to clarify one thing. You know what a 받침 is, right? In case you don't a 받침 is the final consonant sound in a group of sounds (i.e. there are three (or four) characters in one word/part of word). Look at the following examples: 가다 (ga-da) there is only a ㄱ and ㅏ together - this word ends with a vowel sound not a consonant (no 받침). 좋다 (joh-da) there is a ㅈ, ㅗ, and a ㅎ in the first sound - this word ends with a consonant sound (there is a 받침). If you have any questions, let me know. I'll help if I can. ^____^