How to check which node should be posted on which domain? I am looking for a feature which should be able to check the node destination before save it in the database. 
This will be used in multi site  Drupal set up.   

And it must be work like if node 1 has already created in site1 and I want to save node 2 in site2 then it save the node with nid=2 in the site2's node table.

Which means the nid must continues its sequence regardless of domains. Here, database and codebase are same only tables are having different prefixes.
Consider using the Domain Access module. Here's an excerpt from its project page:

The Domain Access project is a suite of modules that provide tools for running a group of affiliated sites from one Drupal installation and a single shared database.
The module uses Drupal's Node Access system to determine what content is available on each site in the network. Unlike other multi-domain modules for Drupal, the Domain Access module determines user access based on the active domain that the user is viewing, rather than which group or site the user belongs to.