I think you wrote your example for simple form as polite form. The simple form would be: 이 강아지 누구 거야?(whose dog is this?) And the answer would be: 그건 우리 강아지야.(it's our dog.) or here you can omit the 그건, so it will be just like 우리 강아지야. And it doesn't always have to end in 거예요. it can be said in many ways. One example: 이건 우리 강아지예요. And I believe you are right in using 이게 and 이. We don't say 이게+noun. 이분 means this person(in polite form): it can mean woman/man/anybody. Usually when indicating somebody officially, when indicating someone you first met, or indicating someone who's older than you. Who's that man? translates to 저분은 누구예요? using (저분= than person). By the way, your sentence is wrong, it should be: 이분은 누구예요? hope this helps.