There are many meanings of 呢. As a final particle, it has the following meanings. 1. To express uncertainty. 你干什么呢？What are you doing? 2. To express certainty! 他没来呢 He has not arrived yet! 3. To ask the question back with stronger tone, 这件事谁不知道呢, Everyone knows of it, don't you? 4. To indicate continuous tense 我正吃饭呢 I am now eating. 5. To indicate a pause, like an ellipsis... 今年呢，比去年收成好 This year... The results are are better than last year

你是在哪儿买的？where are you bought it? 我是坐飞机来的！I come here by air.