We have disabled some of the physical cores for use by the operating system (Windows server usage) in our servers. In our case, the server has 32 cores, but only 24 of those are used by the OS. Do we need to license the remaining 8 cores as well?

Physical cores that are demonstrably disabled for use by the OS do not need to be licensed. For example, if the server has a total of 32 cores and 8 of them are disabled, only 24 cores need to be licensed. However, this exemption has no effect on the minimum number of core licenses required per server (16).

Source: WindowsServer2016LicensingFAQ_as is 2016-09-08