Question: Does any know how to get the RDP version Windows is running with?

Answer: 
Windows RDP uses the executable mstsc.exe located in c:\windows\system32

Simply right click on this file, and go to properties, then click the version tab.

hope this helps.
There can be maybe better way with PowerShell.

First one need complete table of MSTSC build numbers and just compare to output of:

```
(Get-Item C:\Windows\System32\mstsc.exe).VersionInfo.FileVersion

```

And the second one is to read CLSID of registered components which contain also RDP binaries, like that:

```
$Current = 0
$GUID = Get-ChildItem -LiteralPath "Registry::HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID" | Select Name
$GUIDNum = Get-ChildItem -LiteralPath "Registry::HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID" | Select Name | Measure
While($Current -ne $GUIDNum.Count) {
$Path = $GUID[$Current] | Select -ExpandProperty Name
$GUIDName = ((get-itemproperty -literalpath "Registry::$Path").'(default)') 
If ($GUIDName -like 'Microsoft RDP Client Control (redistributable) - version*')
{
Write-Host $GUIDName
}
$Current++
}

```