go to openpose/cmake/Modules/FindCuDNN.cmake and edit:

find_path(CUDNN_INCLUDE cudnn.h
    PATHS ${CUDNN_ROOT} $ENV{CUDNN_ROOT} ${CUDA_TOOLKIT_INCLUDE} /usr/local/cuda/include
    DOC "Path to cuDNN include directory." )

find_library(CUDNN_LIBRARY NAMES ${CUDNN_LIB_NAME}
    PATHS ${CUDNN_ROOT} $ENV{CUDNN_ROOT} ${CUDNN_INCLUDE} ${__libpath_hist} ${__libpath_hist}/../lib /usr/local/cuda/lib64
    DOC "Path to cuDNN library.")