How do I find the Azure PowerShell version?

Get-InstalledModule -Name Az -AllVersions | select Name,Version

It is documented in https://docs.microsoft.com/en-us/powershell/azure/install-az-ps.

This PowerShell cmdlet will get the Azure PowerShell version.

Get-Module -ListAvailable -Name Azure -Refresh

It has a major advantage in which it will be able to return the expected outcome even if the Azure module has not been loaded into the current PowerShell session.

On the contrary, (Get-Module Azure).Version will only work if the Azure module has been loaded into the current PowerShell session before, i.e. by calling any cmdlet from the Azure module in the current PowerShell session, e.g. Get-AzureStorageAccount

Use:

(Get-Module azure).Version

This will return version of installed Azure PowerShell.