So here's the list of available modules in this directory. As you can see DnsShell is there.

PS C:\windows\system32> Get-Module -ListAvailable

Directory: C:\windows\system32\WindowsPowerShell\v1.0\Modules

ModuleType Name                                ExportedCommands                                                             
---------- ----                                ----------------                                                             
Manifest   ActiveDirectory                     {Get-ADRootDSE, New-ADObject, Rename-       ADObject, Move-ADObject...}             
Manifest   AppLocker                           {Set-AppLockerPolicy, Get-AppLockerPolicy, Test-AppLockerPolicy, Get-AppLo...
Manifest   BitsTransfer                        {Add-BitsFile, Remove-BitsTransfer, Complete-BitsTransfer, Get-BitsTransfe...
Manifest   CimCmdlets                          {Get-CimAssociatedInstance, Get-CimClass, Get-CimInstance, Get-CimSession...}
Binary     DnsShell                                                                                                         
Script     ISE                                 {New-IseSnippet, Import-IseSnippet, Get-    IseSnippet}                           
Manifest   Microsoft.PowerShell.Diagnostics    {Get-WinEvent, Get-Counter, Import-Counter, Export-Counter...}               
Manifest   Microsoft.PowerShell.Host           {Start-Transcript, Stop-Transcript}                                          
Manifest   Microsoft.PowerShell.Management     {Add-Content, Clear-Content, Clear-  ItemProperty, Join-Path...}               
Manifest   Microsoft.PowerShell.Security       {Get-Acl, Set-Acl, Get-PfxCertificate, Get-Credential...}                    
Manifest   Microsoft.PowerShell.Utility        {Format-List, Format-Custom, Format-Table, Format-Wide...}                   
Manifest   Microsoft.WSMan.Management          {Disable-WSManCredSSP, Enable- WSManCredSSP,   Get-WSManCredSSP, Set-WSManQui...
Script     PSDiagnostics                       {Disable-PSTrace, Disable-   PSWSManCombinedTrace, Disable-WSManTrace, Enable...
Binary     PSScheduledJob                      {New-JobTrigger, Add-JobTrigger, Remove-JobTrigger, Get-JobTrigger...}       
Manifest   PSWorkflow                          {New-PSWorkflowExecutionOption, New-PSWorkflowSession, nwsn}                 
Manifest   PSWorkflowUtility                   Invoke-AsWorkflow                                                            
Manifest   TroubleshootingPack                 {Get-TroubleshootingPack, Invoke-TroubleshootingPack}

When I run the command to Import-Module DnsShell, I get this error and I dont know why..

PS C:\windows\system32> Import-Module DnsShell
Import-Module : Could not load file or assembly 
'file:///C:\windows\system32\WindowsPowerShell\v1.0\Modules\DnsShell\DnsShell.dll' or    one of its dependencies. Operation is 
not supported. (Exception from HRESULT: 0x80131515)
At line:1 char:1
+ Import-Module DnsShell
+ ~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : NotSpecified: (:) [Import-Module], FileLoadException
+ FullyQualifiedErrorId : System.IO.FileLoadException,Microsoft.PowerShell.Commands.ImportModuleCommand

Note: I would have posted pictures but I needed a rep of at least 10 in serverfault