You should just be able to retrieve the text object value and put it into the rosstalk message.
I'm assuming your script is more than just that one line though, because you dont show how you initialize the rosstalk variable. You also don't mention which event your script is on, so that can change how you would need to write this.. So based on those assumptions, it would be something like this:
dim textobj as xpTextObject
Self.GetObjectByName("TheTextObjectName", textobj)
rosstalk.SendMessage("CUE " & textobj.text)
#XPression