http://woshub.com/install-rsat-feature-windows-10-powershell/
Enable all RSAT modules
Get-WindowsCapability -Name RSAT* -Online | Add-WindowsCapability –Online
Or just AD or DNS or GPO or DHCP
Add-WindowsCapability –online –Name Rsat.ActiveDirectory.DS-LDS.Tools~~~~0.0.1.0
Add-WindowsCapability -Online -Name Rsat.GroupPolicy.Management.Tools~~~~0.0.1.0
Add-WindowsCapability –online –Name Rsat.Dns.Tools~~~~0.0.1.0
Add-WindowsCapability -Online -Name Rsat.DHCP.Tools~~~~0.0.1.0
Add-WindowsCapability -Online -Name Rsat.WSUS.Tools~~~~0.0.1.0
If you use a local WSUS server you might need to disable using it for the install to work
To install RSAT components, you need to temporarily disable the update from the WSUS server in the registry (open the registry key HKLM\SOFTWARE\Policies\Microsoft\Windows\WindowsUpdate\AU and change the UseWUServer to 0) and restart the Update Service.