Click on your Start menu and then click on the gear icon. When the 'new' Settings window appears, click on the Apps icon and then click on the 'Optional Features' link and then click 'Add a Feature'. You'll see a list of apps and 'RSAT: DNS' should be one of the options.
I do remember last year some time when Microsoft first moved RSAT, some of the tools were not included.
Another thought - any chance this is being blocked by a group policy?
So the gear button was the mojo to get to Apps and Features. But alas no sign of RSAT:DNS. It could be I'm out for group policy as you say. I'll see if I can get myself added.
Windows OS
This topic area includes legacy versions of Windows prior to Windows 2000: Windows 3/3.1, Windows 95 and Windows 98, plus any other Windows-related versions including Windows Mobile.