Did you need help with LabJack related calls to get the thermocouple reading, or is that handled in the GetTemp function/method?
Alternative to a while loop you can use a timer that runs at a set interval and gets the reading from the U6:
If you are going to use a while loop you will want it to run in a different thread than your main one. Basically use multithreading where one thread is in the while loop, and other threads are doing something else in your application.
I wasn't sure if you were asking for help with plotting and graphs, but in Qt you can make your own widget to do so or use something like Qwt which provides a framework for plotting:
For Qt related help you will want to do a online search, read Qt documentation and use the Qt forums.