Translation:Where's your house?
I was wondering the same thing; Seems like it's mostly a dialect difference, with 哪儿 being more common in the north, and 哪里 elsewhere? With some footnotes and caveats in more advanced usage? This is what I could find: https://chinese.stackexchange.com/questions/9131/%E5%93%AA%E5%84%BF-vs-%E5%93%AA%E9%87%8C-difference-in-meaning
The tones are different; 那 has the 4th tone (the falling tone) and 哪 has the 3rd tone (the falling-rising tone). Tones are definitely one of the hardest aspects of Mandarin for a learner to master. It's all in the intonation of your voice (which, in Mandarin, is just another aspect that determines meanings of words). The 1st tone is high and level; the 2nd tone is rising; the 3rd tone falls a little then rises; and the 4th tone falls. There's also sort of a 5th tone, which is neutral and just the syllable pronounced quickly (and neutrally). It's a little awkward to explain in writing without audio examples, so I'll link a quick youtube video that gives examples of the 4 tones: