Hi The2abraxis! Good question. So, cognitive psychology, and behavioural neuroscience, are their own subfields of psychology. They actually have no more to do with clinical psych than, say, social psychology or industrial/organizational psychology do. These are research programs. There's no clinical (i.e., practice) component to them.
Researchers in these areas would tend to investigate the basic mechanisms of, say, attention, memory, judgment/decision-making, and emotion (to name a few concepts) at the behavioural and neural level. Though some researchers might link their work to psychopathology or investigate these phenomena in clinical populations, but the focus is very much *not* on assessment, therapy or rehabilitation (unlike with clinical neuropsych).
Are you an undergrad psych major? If so, you should consider taking courses in Cognitive Processes (related to cognitive psych) and/or Biological/Physiological Psychology (related to behavioural neuroscience). A course in the History of Psych might not hurt, too. Psych's a broad field, and you'll need to know this stuff for the Psych GRE.
