呢 ne is placed at the end of a sentence. It can be used in the following situations:
1. To bounce a question or statement back to the person you are having a conversation with, as in:

A: 你 好吗 nĭ hăo ma ?

how are you?
B: 我 很 好。你 呢 wŏ hěn hăo. nĭ ne?

I am very well, and you?
2. To ask the question where? as in 我 的 书 呢 wŏ de shū ne where is my book?
3. To reinforce questions formed with a question-word [who? what? which? when? why? where?] and to show that a speaker really wants to know the answer, as in:

他 是 哪 国 人 呢 tā shì nă guó rén ne what nationality IS he?

你 看 的 是 什 么 书 呢 nĭ kàn de shì shénme shū ne what book ARE you reading?

你 去 哪 儿 呢 nĭ qù năr ne where ARE you going?