Since I couldn't find an answer here, I would say that the right answer is:
There is no such thing in Linux/Ubuntu.
If you want to know the amount of key strokes and clicks you did, you will have to install some third-party program, that may or may not use your information for God knows what.
Key loggers do not have what I'm looking for: they only record the phrases I typed and the program name in a text file, like:
15/07/2005 | MSN Messenger | Text: Hey there, want to chat?<CTRL><ENTER>
So, I would have to write a shell script to extract only the typed part, and count every letter individually. But how about mouse clicks? Function-keys?
In other words, a key-logger does not fit my needs.
I did manage to find another kind of program, specifically designed for this purpose, with heat maps and graphics for mouse and keys, but as I mentioned above, the download site is not that trustworthy, it isn't available in the Ubuntu market store, and it demands a Facebook login ....