An appositive is a word or phrase that refers to the same idea as another word or phrase in proximity. The phrase “my friend Robert” contains two appositives, because “my friend” and “Robert” are two ways of identifying that person. Here you can omit the commas totally or you can use them in the manner you have already used. "My friend, Robert, is very honest." It is correct. "Hard-work" or "hard-working" should not have the hyphen. "Hard-work" should be "hard work" as these are two different words and not a single word. "Hard-working" should be "hardworking" as it is single word. "Hardworking" is an adjective where in words "hard work," work is a noun and "hard" is an adjective. My friend, Robert, is very hardworking. My friend, Robert, is a very hard worker. Both these sentences are correct. His hard-working paid him, and he passed exams. You should say "His hard work paid off and he passed exams."

Comma should be used after Robert. Not before Robert. Comma is used to show a pause in the sentence. It is also used to separate the different elements in a sentence. Correct Sentence- My friend Robert, is very honest. http://grammar.ccc.commnet.edu/grammar/commas.htm 'Hard-Work' is the action, 'Hard Working' is the action in progress. These sentences are correct- My friend Robert, is very hard working. My friend Robert, is a hard worker. His hard work paid off, and he passed his exams.