Does each code of an ADC have a DNL value?
Yes, there is a DNL value for each code of an ADC, except of the code at each end of the ADC range.  ADC data sheets contain specifications for the DNL.  The DNL specification refers to the maximum and minimum values of the DNL; that is, the most positive and most negative DNL found at any code in the ADC range.

Many ADC data sheets also contain plots of the typical DNL across the ADC range, as shown here for a 12 bit converter (4096 codes, 4094 DNL values).