What is 'man' here?
The colonel and his fellows invade Mayor Orden's village and they are going to shoot a man who does not obey them in the square.
Lanser: Colonel Lanser
Loft: Captain Loft.
Orden: Mayor Orden

Captain Loft gathered his papers and Lanser asked, "In the square, Captain?"
"Yes, in the square. It must be public," Loft said.
And Orden said, "I hope you know."
"Man," said the colonel, "whether we know or not, it is what must be done."

Is 'man' here an interjection like wow or it refers to a person?

Question

What is 'man' here?
The colonel and his fellows invade Mayor Orden's village and they are going to shoot a man who does not obey them in the square. 
Lanser: Colonel Lanser
Loft: Captain Loft.
Orden: Mayor Orden

Captain Loft gathered his papers and Lanser asked, "In the square, Captain?"
"Yes, in the square. It must be public," Loft said.
And Orden said, "I hope you know."
"Man," said the colonel, "whether we know or not, it is what must be done."

Is 'man' here an interjection like wow or it refers to a person?

Answer

I agree with V.I. It's strange, as is the form of the rest of the sentence.

Answer

Man refers here as a person who is showing resistance of being disobedient.

Answer

I honestly do not know.  It is written as if indeed it is an interjection, but that would imply modern, informal dialogue. Almost slang.   I'm not a linguist but I think 'man' as an interjection didn't arrive until the 1970s?

Answer

Hi how are you?