> 「今日は何する **の** ？」

I found this sentence by a Japanese person on a Japanese speaking website. I
am aware that の is the possessive particle in Japanese, and allows for
sentences such as

> 「僕 **の** 娘は店に行って靴を買います。」

But what I don't understand is why の is used at the end of the first sentence
without directly stating anything. Why exactly is の being used like that, and
what does it mean?
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2015-11-29T18:17:09.497
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2015-11-29T21:07:56.520
2015-11-29T21:07:56.520
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question
meaning particle-の questions
Why in this sentence is 「の」used in this fashion?