Koreans understand you when you ask using the -나 ending. This -나 ending is standard in the South, but not in 서울. I'd suggest you use the -어 ending because it's most common. I don't think we use the -니 ending very often nowadays. Adults use -니 when talking to a little kid, so it doesn't sound pleasant if you aren't a little kid. Also, you can't use -니 with someone older(even if it's your close friend) Mom: (to her son) 숙제 다 했니? Did you finish your homework? Jane : (talking on her cell phone) 너 지금 어디 있어? Where are you know? Joe : 밖에 있어. I'm outside. (They're the same age) Southerner 1 : 돈 좀 있나? Do you have some extra money? Southerner 2 : 와? Why?

"-니?" is used for asking someone younger. "-나?" is a standard form. It can be used for talking to oneself. Southern South-Korean like Pusan use it for asking.

thaiholic: thank you very much! ^^ Bryan Cho: I'm sorry for the confusion TT

있나.. 있니.. 있습니까.. same meaning. 있나?, 있니?(do you have?) only between friends, not formal. 있습니까? formal. 있나, 있니.. ending '나' and '니' is almost same, no meaningful to distingulish, but i strongly recommend you to use '니'.

I can't make sense your question. T.T