it drops its action here: c:\program files(x86)\windows kits\10\
and you can find the d3d12 sdk as a separate download in that directory. you can just point to the headers and libs in this directory for your dev work.
i'll pretend that was easy to figure out.
changes continue for the SDK, new location is same high level directory but you have to dig a bit more to find the .h and libs:
c:\Program Files (x86)\Windows Kits\10\Include\10.15063.0\um
my guess is um is for unmanaged, as in fast, unmanaged code
IMO the upgraded directory clarity is a good thing.