I am using Search catalog objects in catalogapi, but the values returned in sandbox and production are different.
location_overrides is returned in sandbox but not in production. why is that?
This is the expected behavior. The sandbox objects will have different IDs from the production objects. 
Where is it mentioned in the documentation?
Our sandbox documentation covers mentions that the Square Sandbox consists of a free, isolated server environment, a set of Sandbox seller test accounts, and a Sandbox Seller Dashboard for each account. While it doesn’t specifically say anything about items its a separate account and with Square’s account model, each account will have separate item IDs.
the current,
Batch retrieve inventory counts is used to retrieve inventory in bulk.
In order to narrow down the target, Sandbox obtains location_ids and catalog_object_ids from Search catalog objects.
How do I get location_ids and catalog_object_ids in Production?
With the Catalog API and Locations API you can get the production IDs. 