This simple line dumps all paths to all desktops found in any of the local user profiles – just make sure you are running the line with Administrator privileges to see other peoples‘ profiles:
Resolve-Path -Path C:\users\*\Desktop -ErrorAction SilentlyContinue
If you just would like to get the user names for those profiles that have a „Desktop“ folder, try this:
Resolve-Path -Path C:\users\*\Desktop -ErrorAction SilentlyContinue | ForEach-Object { $_.Path.Split('\')[-2] }
The code takes the paths and splits them at the backslash, producing an array of path components. Index -2 is the second-last component, thus the name of the user.