Could somebody advise the best way to add correct Schema.org markup for the page where the user can buy some product? I am adding the Product tag there (for Rich Snippets). 
I would like to add possibility to ask questions about this product, but I didn't find what properties I could use as embedded items.
Example:
<div itemscope="" itemtype="http://schema.org/Product">
    <meta itemprop="brand" content="Brand">
    <meta itemprop="url" content="URL">
    ......
    <div id="question1" itemprop=??????? itemscope="" itemtype="http://schema.org/Question">
         ......
        <div id="answer1" itemprop=??????? itemscope="" itemtype="http://schema.org/Question/Answer">....</div>
        <div id="answer2" itemprop=??????? itemscope="" itemtype="http://schema.org/Question/Answer">....</div>
    </div>
    ...
    <div id="question10" itemprop=??????? itemscope="" itemtype="http://schema.org/Question">
        ......
        <div id="answer1" itemprop=??????? itemscope="" itemtype="http://schema.org/Question/Answer">....</div>
        <div id="answer2" itemprop=??????? itemscope="" itemtype="http://schema.org/Question/Answer">....</div>
    </div>
</div>