Thank you for including the demonstration link to your project. You should use the
log command on the elements whose events you are interested in recording. In your case, you want to know when participants press the spacebar key, and when the Text elements are printed, so you should use that command on your Key and Text elements. One simple way of doing it is to add them as default commands to the top of your trial:
I tested it and it adds 20 lines per trial to your results file. Logging both elements types is a little redundant, so you could choose ton only log the Key elements, for example (in which case it could be a good idea to name those Key elements, to make it easier to read your results file). Then you simply subtract EventTimes to get reading times.
Let me know if you have questions