Hi @Prateek Rana ,
Firstly there is no built-in initiative with the name "Azure security benchmark" or "ASC default".


There is policy assignment with the name starting with "ASC Default".

In case you are looking for command to get policy assignment details along with assigned by information then use below command.
Get-AzPolicyAssignment -Id "/subscriptions/xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/providers/Microsoft.Authorization/policyAssignments/SecurityCenterBuiltIn" | Select-Object @{Name="DisplayName"; Expression={$_.Properties.DisplayName}}, @{Name="Name"; Expression={$_.Name}}, @{Name="ResourceId"; Expression={$_.ResourceId}}, @{Name="Scope"; Expression={$_.Properties.Scope}}, @{Name="EnforcementMode"; Expression={$_.Properties.EnforcementMode}}, @{Name="AssignedBy"; Expression={$_.Properties.Metadata.AssignedBy}}, @{Name="CreatedBy"; Expression={$_.Properties.Metadata.CreatedBy}}, @{Name="CreatedOn"; Expression={$_.Properties.Metadata.CreatedOn}}, @{Name="ExcludedOutOfTheBoxStandards"; Expression={$_.Properties.Metadata.excludedOutOfTheBoxStandards}}, @{Name="Description"; Expression={$_.Properties.Description}}

If that's not what you are looking for and as explained here and here if you are looking for effect details of policies that are part of initiative, then it's provided as part of parameters properties as shown below. To fetch those details you might have to come up with a script and then export it to csv file.


If you think fetching effect details from parameters properties of Get-AzPolicySetDefinition cmdlet is difficult then you may fetch the same by calling Get-AzPolicyDefinition cmdlet in a loop for each initiative something like shown below.
$objResults = @()
$arrResults = @()
$GetPSDs = Get-AzPolicySetDefinition
foreach ($GetPSD in $GetPSDs) {
$GetPDIDs = $GetPSD.Properties.PolicyDefinitions.PolicyDefinitionId
foreach ($GetPDID in $GetPDIDs) {
$GetPD = Get-AzPolicyDefinition | ?{$_.PolicyDefinitionId -eq $GetPDID}
$objResults = New-Object PSObject -Property @{
PolicySetMetadata = $GetPSD.Properties.Metadata;
PolicySetDisplayName = $GetPSD.Properties.DisplayName;
PolicySetDescription = $GetPSD.Properties.Description;
PolicySetType = $GetPSD.Properties.PolicyType;
PolicySetDefinitionID = $GetPSD.PolicySetDefinitionId;
PolicyMetadata = $GetPD.Properties.Metadata;
PolicyDisplayName = $GetPD.Properties.DisplayName;
PolicyDescription = $GetPD.Properties.Description;
PolicyType = $GetPD.Properties.PolicyType;
PolicyDefinitionID = $GetPD.PolicyDefinitionId;
AvailableEffects = [string]$GetPD.Properties.Parameters.effect.allowedValues;
}
$arrResults = $arrResults + $objResults
}
}
$arrResults | Export-Csv -Path "C:\xxxxxx\xxxxxxx\xxxxxxx\PSD_PD_Output.csv" -NoType
Output:

Note that execution time of above provided script would depend on the number of policies inside an initiative and the number of initiatives in your environment. If the execution time is more then you may have to tweak the script to execute faster with the help of Start-Job cmdlet so that starts an asynchronous job or else try parallel processing using foreach parallel or any other approach which completes the execution faster.