It depends on the version of the kernel that's used on the system in question.
I have .exe and .pdb for the following in my Symbol folder:
ntkrnlmp
ntkrnlpa
ntkrpamp
ntoskrnl
And, as I recall, they may all be referenced as ntoskrnl once installed in the system (so, if your system needs ntkrnlpa, it'll be renamed to ntoskrnl during setup)
The versions are pointed out in the Overview here: https://en.wikipedia.org/wiki/Ntoskrnl.exe
But I seem to recall reading it in Windows Internals a while back (can't recall where in it)
This topic tends to verify that the particular version is renamed to ntoskrnl.exe at installation: https://www.osronline.com/showthread.cfm?link=156965
