Neurologists study the nervous system.
They study diseases.
a geneticist
Biologists.
It depends on what kind of scientist it is. For example, botanists study plants.
An Anatomist - They study anatomy.
a physist
A herpetologist studies lizzards and snakes.
Computer Science and IT (Information Technology)
Zoologists study animals.
An apiologist.
Astronomer
All scientist study science so every one you could think of :)