It would help if I understood the context of what it is you're trying to do.
If you want to use the {TASK(PrevTask,Name)} variable, you would have to use that as part of a 2nd task in the same job (or at least thats my understanding)
So... Task1 does something, then Task2 does something but uses the 'PrevTask,Name' variable for something.
If you want a reference somewhere that will pull the name of a specific task from anywhere in VisualCron, whether its part of the active job or not.... click the little 'variables' button and expand the tree out until you find the exact task.
See Screenshot, it should make sense.
I have a job called 'Test Rename' and in that job I have a task called 'Rename Files'. I've selected this 'Rename Files' task and you'll see the resulting variable down below that will pull that name.
bbusse attached the following image(s):