If what you're trying to do is what I think it is, you should be able to find the data (in this case the text) by calling objectname.variable name. So as an example, if you had a sprite called "Player" and wanted a textbox to display the life of 'Player' you would have an action that set the text of textbox to player.health (with no quotation marks around it so it was recognized as an expression).
If you are doing this for multiple objects/instances, make sure you use something to pick the correct instance, such as 'pick nearest' or 'pick nth instance' or some such.
Hope you have some luck in trying to solve your issue!
Regards,
Gideon