Is it possible to prompt for restarting the machine after installation using WiX?

<?xml version='1.0' encoding='windows-1252'?>
<Wix xmlns='http://schemas.microsoft.com/wix/2006/wi'>

    <Product
        Name = 'Sample App'
        Id = 'PRODUCT-GUID-HERE'
        UpgradeCode = 'UPGRADE-GUID-HERE'
        Language = '1033'
        Version = 'YOUR-APP-VERSION-HERE'
        Manufacturer = 'YOU!'>

        <InstallExecuteSequence>
            <ScheduleReboot After="InstallFinalize"/>
        </InstallExecuteSequence>
    </Product>
</Wix>

I think I got it.

Yes. See the documentation for the REBOOT property in Windows Installer.

i.e.:

<Property Id="REBOOT"><![CDATA[Force]]></Property>