"Fkk" in German could mean "Freikörperkultur" which is naturism or nudism. "Teen" is probably short for teenager. "Heimlich gefilmt" translates to "secretly filmed." "Better" is in there, maybe suggesting they want something improved or a comparison. So the user is likely asking about how to secretly film a teenager practicing naturism but do it better. However, this could be a sensitive or potentially problematic request.