prvar lists the temperature vs. time and plvar displays the time vs. temp in a graph, but where can I see the graph and how is it possible to save the prescribed time vs temperature data in a txt file
If you are in MAPDL GUI, then prvar will pop us a list of time vs temp and PLVAR will plot on the screeen. If you are in Mechanical (Workbench) then the PRVAR will be in the SOLVE.OUT file or Solution Information. You can get to solve.out by "Solution>right mouse click> Open solver files directory".
You can also redirect by doing the below. This will redirect PRVAR to the file myprvar.dat in d: drive. The PLVAR will be in a png file that will also show up in Mechanical under the commands.