HOTSPOT
Your network contains one Active Directory forest named contoso.com and one Active Directory
forest named adatum.com. Each forest contains a single domain.
You have the domain controllers configured as shown in the following table.
You perform the following three actions:
Create a user named User1 on DC3.
Create a file named File1.txt in the SYSVOL folder on DC1.
Create a Group Policy object (GPO) named GPO1 on DC1 and link GPO1 to Site2.
You need to identify on which domain controller or controllers each object is stored.
What should you identify? To answer, select the appropriate options in the answer area.
Answer: 
Explanation:
Understanding the Global Catalog
https://technet.microsoft.com/en-us/library/cc730749.aspx
Y N Y
Y N N
N Y N
N Y N
The user object and GPO surely only exist in each domain.
The GC’s contain a subset of attributes about the user not the actual user object itself.
Also the site information for the GPO (gplink information) will replicate forest wide but the actual GPO object only exists in the domain so is not replicated outside the domain. Have indicated the summary in the article that was linked to below.
for me the answers are :
DC1 v _ v
DC2 v _ v
DC3 _ v _
DC4 _ v _
Perhaps it depends on your definition of what an “object” is in the question. Happy to be corrected on this one.
GPO = GPT + GPC
•GPC – Stored in the Active Directory Domain partition under System\Policies. Replicated to all DCs in the domain. (not forest)
•GPC – Stored in SYSVOL and replicated by FRS or DFSR to all DCs in the same domain. (not forest)
•GPLink – Stored in Active Directory on the object where a GPO is linked.
◦If a GPO is linked to the domain or OU object the GPLINK is replicated domain-wide (with the Domain partition).
◦If a GPO is linked to a site object it is replicated Forest-wide (with the Configuration partition.)
Agree with ChaserZX
DC1 (Contoso)Y N Y
DC2 (Contoso)Y N Y
DC3 (Adatum) N Y N
DC4 (Adatum) N Y N
Sysvol replicates to all DCs in contoso, so this includes the file created in sysvol, and the GPO1 template stored in sysvol.
User account replicates to all DCs in Adatum, a seperate forest to Contoso, so therefore will not replicate to any DCs in contoso.
You are right.
ChaserZX – you are right. Boundare of forest are the highest level boundary in replication. Nothing can went out without special and intentional actions. Being on the same Site (physical location) does not changing case. In meaning of sites in AD, either – it is because object from another-foregin forests can not be added to AD site.
why are we assuming the sites have site links??????????????? where in the question does it state this.
If seperate Site Links are not mentioned, we must/can assume DefaultSite is used