I have a question regarding the intensity peak in an XRD graph for a material that has a preferred orientation along . which "hkl "will have the highest peak and which ones will have lower peak?
Generally, the layered materials show preferred orientation which affects the intensity of the particularly  reflections. In this case, the intensities of the other reflections are lower compared to  reflections. The changes in the intensity depend on the microstructure. So if a material has a preferred orientation along 001, the highest reflection is 001, but the lower reflections depend on the structural parameters such as the space group, atomic positions, atomic displacement parameters, occupancy, etc.
Disclaimer: I’m not an XRD expert.