Which one is correct ??

[weediamond]

Jack of all trades, master of nothing OR Jack of all trades, master of none

[Clanad]

One site says ""Jack of all trades and master of none. Said of someone who has a basic familiarity with many things but isn't an expert at anything. In 1612, appeared in 'Essays and Characters of a Prison' by Geffray Mynshul. The phrase has been in use in the United States since 1721..." From "Random House Dictionary of Popular Proverbs and Sayings" by Gregory Y. Titelman (Random House, New York, 1996).

The "Morris Dictionary of Word and Phrase Origins" by William and Mary Morris (HarperCollins, New York, 1977, 1988) gives further insight into the phrase:
"jack of all trades, master of none" has been around at least since 1600. Anyhow, the 'jack of all trades' part of it was circulating at that time and, generally speaking, it was a term of praise, rather than disparagement, as it is today. One writer noted 'Old Lewis' was sort of 'Jack of all trades,' which made the rest of the tradesmen jealous.' 'Jack,' in those days was a generic term for 'man.' Later the 'master of none' was added and the expression ceased to be very flattering. Today it is used to describe a person whose knowledge, while covering a number of areas, is superficial in all of them. If you want a very elegant word to describe such people, call them 'sciolists' (pronounced SY-uh-lists). They won't know what you're saying and will probably take it as a compliment." With that etymology I'd go with "...master of none...

[THECORBYLOON]

I would say it's "master of none" as "master of nothing" would refer to anything and not only a trade.

[waggstar]

It's master of none. Master of nothing doesn't make any sense grammatically, and I've never heard of it, (not that I'm any authority on such things), but I'd bet my house that it was 'master of none'.