var propValue = pega.u.d.getProperty("propertyName");
var propValue = pega.u.d.getProperty("propertyName", "pageName");
Just make sure these properties are present in the UI also since this is a client side api. If you need something from server side (which is only on clipboard page) you can use safeURL to invoke activity in async mode and get the value.
just as some addition - there's "hidden" control available to handle such use cases. You need to have this property exposed in UI - if you don't need it to show up in your UI, this is the best approach to use.
Please note, in this case you need request to server, what's more this property will be fetched from Clipboard. In case of client-side changes of this property they could have different value on server (until you submit the form).