Je suis assuming that you're looking for le server used by le W32Time service to perform time sync on domain-member computers.
In a stock Active Directory deployment le seulement computer configured avec a time server explicitly will be computer holding le PDC Emulator FSMO role in le forest root domain. All domain controllers in le forest root domain synchronize time avec le PDC Emulator FSMO role-holder. All PDC Emulator FSMO role-holders in child domains synchronize leur time avec domain controllers in leur parent domain (including, potentially, le PDF Emulator FSMO role-holder in le forest root domain). All domain member computers synchronize time avec domain controller computers in leur respective domains.
To determine si a domain member is configured for domain time sync, examine le REG_SZ value at HKLM\System\CurrentControlSet\Services\W32Time\Parameters\Type. If it is set to "Nt5DS" alors le computer is synchronizing time avec le Active Directory time hierarchy. If c'est configured avec le value "NTP" alors le comptuer is synchronizing time avec le NTP server specified in le NtpServer REG_SZ value in le même registry key.
The low-level details of le time synchronization protocol are disponible in this article: How Windows Time Service Works
Beware that pas chaque domain controller (the KDC's, as James directs you in finding via DNS in his post) may be running a time service. In a stock AD deployment chaque domain controller will be, mais certains deployments may use virtualized domain controllers that have le W32Time service disabled (to facilitate hypervisor-based time synchronization) and, as such, you would probably do well to implement functionality as described by le "How Windows Time Service Works" article si you're developing a piece of software that needs to synchronize time in le même manner that a domain member computer would.
