There is probably more than one way to skin this particular cat, but if you go into:
Computer Management > Storage > Disk Management
All of your drives will be listed as
Disk 1, etc along with their drive letter or mount point.
smartctl allows you to reference drives by that physical disk number with the identifier
X is the disk number) instead of the drive letter (amongst other identifiers).
For example, if the disk corresponding to your desired mount point was
Disk 8, the following command should work:
smartctl.exe -s standby,now /dev/pd8
But unfortunately I don't see that there's a way to reference the mount point directly from the command line by directory name, to answer your main question.
But if you wanted to script it, you can enumerate physical drives and letters/mount points and then parse that info to get the physical disk, then pass that to
smartctl. I haven't done it myself, but this seems like a good of a starting place as any: