Which one is correct?
Hard-working OR Hardworking
No, it should be 'hard-working'. Check the dictionary please.
There are two choices: hard-working or hardworking. As long as the two words are together in some form or another, the combination works. These are hardworking, or hard-working words.
About the hyphen: "Hard-working" should always have a hyphen, at least in American English. Decisions about hyphenation are too complex and too dependent on context for Word to make them correctly every time.But it appears that not all Americans seem to agree on the hyphen. From Preferred Spellings and Capitalizations: References: Office of Creative Services: Indiana University