Hi Rakesh,
When you create a sub object to an object, you could navigate to that sub object's page, only through it's respective parent object, in your case, the the Parent Project's properties menu, to reach the ABC list page. This is as per functionality.
As an idea, you could create a portlet on the sub object, (either object based or query based), which will display in a single page all the instances of this custom object. If that helps you or is applicable for your business case.
Example:
A custom sub object of project -> proj_sub_obj is created:
Data instances are inputted for couple of projects, on two separate projects:
A portlet is created on the custom object:
The respective custom object could be navigated through using links from the portlet. The portlet, sub objects, viewing could be governed by access rights.
Regards,
Samik