Hi Binod, yes, I see what you're trying ot do here. The short answer is that I don't think that the out-of-the-box REST API is going to behave the way that you want. For content, the API is focussed on the CMS_Tree structure, and your linked document effectively is a new item in here. Your calling service may need to do some work here by calling the API again when NodeLinkedNodeID is not null.
For example, on my test site, when I call http://localhost/cx10/rest/content/site/blank/en-GB/all?classnames=cms.news&columns=nodealiaspath,DocumentName,DocumentNamePath,NodeAliasPath,NodeLinkedNodeID
I see the following results:
<cms_documents>
<cms_news>
<nodealiaspath>/News/News-article-1</nodealiaspath>
<DocumentName>News article 1</DocumentName>
<DocumentNamePath>/News/News article 1</DocumentNamePath>
</cms_news>
<cms_news>
<nodealiaspath>/News/News-article-2</nodealiaspath>
<DocumentName>News article 2</DocumentName>
<DocumentNamePath>/News/News article 2</DocumentNamePath>
</cms_news>
<cms_news>
<nodealiaspath>/News/News-article-3</nodealiaspath>
<DocumentName>News article 3</DocumentName>
<DocumentNamePath>/News/News article 3</DocumentNamePath>
</cms_news>
<cms_news>
<nodealiaspath>/News/News-article-4</nodealiaspath>
<DocumentName>News article 4</DocumentName>
<DocumentNamePath>/News/News article 4</DocumentNamePath>
</cms_news>
<cms_news>
<nodealiaspath>/News/News-article-5</nodealiaspath>
<DocumentName>News article 5</DocumentName>
<DocumentNamePath>/News/News article 5</DocumentNamePath>
</cms_news>
<cms_news>
<nodealiaspath>/Home/News-article-1</nodealiaspath>
<DocumentName>News article 1</DocumentName>
<DocumentNamePath>/News/News article 1</DocumentNamePath>
<NodeLinkedNodeID>1384</NodeLinkedNodeID>
</cms_news>
</cms_documents>
The last item in the list here is a linked document, so I know I need to retrieve it using http://localhost/cx10/rest/content/site/blank/en-GB/all?classnames=cms.news&columns=nodealiaspath,DocumentName,DocumentNamePath,NodeAliasPath,NodeLinkedNodeID&where=NodeID=1384
If you need something more tailored than that, it's my understanding that you're going to create something custom.