The configuration DC:
https://learn.microsoft.com/en-us/powershell/module/exchange/set-adserversettings?view=exchange-ps
The ConfigurationDomainController parameter specifies the fully qualified domain name (FQDN) of the configuration domain controller to be used for reading Exchange configuration information in this session.
DSACcess Event 2080 tells you what DCs are being used:
https://learn.microsoft.com/en-us/exchange/troubleshoot/administration/msexchangedsaccess-event-id-2080
IF you want to exclude a DC from Exchange:
set-exchangeserver <Exch Server> -StaticExcludedDomainControllers DC1, DC2
https://learn.microsoft.com/en-us/powershell/module/exchange/set-exchangeserver?view=exchange-ps