As the percentage of rGO increases in ZnO-rGO composite the peak intensity of D and G band decreases and most of peaks in ZnO dissapears ,only one peak at 432cm-1 remains. how to interpret this results in terms of band gap in ZnO.
In order to say something significant about the above peaks, you should indicate the method for preparing the compositions. Zinc oxide and reduced graphene oxide compozite can be obtained in several ways...
According to your Raman spectra, I believe the coating of rGO diminishes the Raman peaks of ZnO. The peaks of the rGO are not well-resolved, possibly due to the small size of your rGO or the Raman spectrometer is not focused well.