The only actively maintained OpenCL code in Blender is the Cycles kernel. However any OpenCL specifics are abstracted away, to make the same code compile to CUDA and C++.
So there is no area of Blender where you can immediately apply OpenCL knowledge. To contribute to Blender it’s probably better to think of a specific feature or area you want to improve and figure out what is needed for that, rather than starting from a specific technology.