What is the charger voltage graph while charging Lithium battery with CC/CV approach?
Looking closely to the CC/CV transition of the graph, there is a sharp
  turn in the battery current. If the internal resistance of the battery
  is not changing that sharp - which I think it's not the case -, this
  is a good indication of a sharp voltage change on the output of
  charger.


The charger is connected directly to the battery, so their voltages are always equal. In the CC phase the battery controls the voltage as it charges up. The charger merely responds by raising its voltage to keep the current going. 

If you compare the battery voltage curves during CC charging and discharging, you will see that they are almost a mirror image of each other. That is because in both cases the battery's voltage is determined by its state of charge (with a slight difference due to voltage drop across the battery's internal resistance, which is positive during charging and negative during discharge).   

At the CC/CV transition there is no change in charger output voltage, which then remains constant in the CV phase. At this point the charger is controlling the voltage, by decreasing charging current to prevent the battery voltage from increasing.


  It might be quite possible that the charger exceeds the CV value right
  before the CC/CV transition point to keep the current constant


It shouldn't. The charger may need to produce a higher voltage internally to overcome resistance in its components and wiring, but it should not exceed the CV value at the battery terminals. 


  Is there any point in the charging process that the output of the
  power source exceeds the CV limit in CC stage?


No. Power output is maximum at the point where both current and voltage are maximum, which is at the CC/CV transition.