Seeing the php dump I think the session variable you want is $_SESSION["userdata"][0]["email"]
.
So in your script it would then become
<script type=“text/javascript”>
var Tawk_API=Tawk_API||{};
Tawk_API.visitor = {
name : '<?php echo $_SESSION["userdata"][0]["FirstNames"] ?>',
email : '<?php echo $_SESSION["userdata"][0]["email"] ?>'
};
var Tawk_LoadStart=new Date();
// rest of the tawk.to widget code
</script>
App Connect expressions in script blocks will not work, but PHP can be used inside the script blocks.