Sonny is a custom made NS-5 robot built by Doctor Alfred Lanning. His purpose was to assist Lanning in planting a trail of bread crumbs that lead to a problem at the heart of the USR corperation. To that end he was built using a denser alloy than normal NS5s and he has an extra positronic core which allows him to violate the three laws of robotics.
In terms of capabilities he doesn't really have any exotic capabilities and is just all around more capable than a real world human.