what is the difference between
inu ga kowai, deshou? and
inu ga kowai desu, ne?
when which should be used?

Question

what is the difference between
inu ga kowai, deshou? and 
inu ga kowai desu, ne?
when which should be used?

Answer

deshou is usually used to express an uncertain affirmation, but it also works as a reminder, like: "but weren't you afraid of dogs?"
desune is just used as a normal question in which the speaker thinks the other person is afraid of dogs: "you are afraid of dogs, aren't you?"

Answer

Deshou でしょう is a ultra polite form of   だろう  darou.

Answer

"inu ga kowai no deshou?" and "inu ga kowai no desune" are almost same meaning. "deshou" sounds softer than "desune".