I know it’s probably easy but I can’t find how to do this…
I have audio pieces which need to be separated by exactly a second, two seconds, three seconds, etc, and I’m not sure how to do it on Cubase Elements 8.
Help please ? 
Right-click your timeline and you should be able to select “seconds/minutes” as your format.
Then, with snap set to “grid” (funny icons in your top section above timeline) you should be able to click your mouse and it will snap to seconds.
Or you could bring up your transport, right-click to change the format to “seconds/minutes” and enter it by numbers. (double-click the number fields).