The Reports menu in ZEMAX provides two different reports which may be used to return detailed index data.  Specifically, the Surface Data report (Reports > Surface Data) lists the index of refraction data for each design wavelength for the selected surface number.  In the case below, Surface 1 has a glass type of SK2, and the index for each of the design wavelengths is reported:

The Prescription Data Report (Reports > Prescription Data) on the other hand, will display index data at each wavelength for every surface in your design.

In addition to the reports, the index of refraction can be returned in the Merit Function Editor via the INDX operand.

The only input values for this operand are the surface number and wavelength.  And, as is the case for any optimization operand, this data is also then accessible with the ZEMAX Programming Language through the OPEV() or OPER() functions.