Do you have any ideeas how can i resolve this type of exercise ? Some examples ?.

 

Do you know how to bias a Zener diode to get it to give its output voltage?
If not I suggest you look up some basic theory about that.

 

You can start by understanding the behavior of an ordinary diode when it is forward biased and when it is reverse biased. Draw a current versus bias voltage if you need to do that.
The do the same thing for the Zener diode.
In each of the circuits you can establish the bias condition of each diode and draw the appropriate conclusions.