Check whether the AlwaysOn feature is enabled. You can do this from the GUI by launching SQL Server Configuration Manager, right-clicking on the SQL Server database engine service, and selecting Properties. Click on the AlwaysOn High Availability tab:

You can also do this using PowerShell by running the following code:

$instanceName = "SQL01"
$server = New-Object Microsoft.SqlServer.Management.Smo.Server -ArgumentList $instanceName

#check AlwaysOn
$server.IsHadrEnabled

To check this feature against multiple nodes, you can use the following code snippet:

$nodeNames = Get-ClusterNode |
             Select-Object –ExpandProperty Name
Foreach-Object ($instanceName in $nodeNames) {
   $server = New-Object Microsoft.SqlServer.Management.Smo.Server -ArgumentList $instanceName

   #check AlwaysOn
   $server.IsHadrEnabled
}

Perform the following steps to enable AlwaysOn in SQL...