What does it mean by cognitive design in modern artificial intelligent? and what is the difference between cognitive and reactive agents?

The most important distinction is between "Cognitive Agent" and "Reactive Agent". A cognitive agent is an agent with cognitive capabilities (mental states, knowledge, belief, ... and cognitive processes like reasoning, learning, problem solving, planning, natural language processing, etc.). Since cognitive agents are considered in general in the context of Multi-Agents Systems, communication becomes another important cognitive process. A reactive agent is an agent with perceptual and acting capabilities with a kind of Stimulus-Response behavior.