DSQUERY server can be used to locate global catalogs
To search the entire forest
dsquery server -forest -isgc
To locate global catalogs in your current (logon) domain
dsquery server -isgc
To locate global catalogs in a specific domain
dsquery server -domain NISHANT.BIZ -isgc
Here, you search for global catalog servers in the tech.cpandl.com domain.
You can also search for global catalog servers by site, but to do this, you must know the full site name, and cannot use wildcards. For example, if you wanted to find all the global catalog servers for Default-First-Site-Name, you would have to type
dsquery server -site Default-First-Site-Name .
The resulting output is a list of DNs for global catalogs, such as