to calculate the damage index, I need maximum and ultimate ductility but I don't know from which option in software ETABS I can find both the values.
If you mean the modified Park & Ang damage index, it is based on the rotation and the dissipated energy.
The ultimate rotation depends on the backbone curve of the hinge that you define. It can be considered the CP (collapse prevention) limit state for example. The maximum rotation is the maximum rotation experienced during the time history analysis. You can check it from the hinge responses.
In general doing this for the whole structure in ETABS or SAP2000 is a bit tricky. If you use OpenSees, it is easier to write a post-processing code in MATLAB and calculate everything automatically.
Have nice day!