An Australian 1989 Twenty Dollar note (Phillips/Fraser)(serial EVJ to EYD), uncirculated and in absolute mint condition could fetch anything up to $145 AUD. If it has been circulated but still in good condition, it might fetch anything from $28 to $50 AUD.
Any banknote with a "genuine" printing flaw would have some value, above the usual, as a collectible banknote.
Genuinely flawed banknotes are not necessarily known about or documented until somebody turns up with one, since they are an "accident" of the printing process, and have escaped detection during quality control at the printers therefore, a valuation cannot be anticipated.
Any valuation would also depend on the nature and extent of the printing error.
A reputable coin dealer should be able to identify and confirm the banknote as genuine and make a valuation.
Australian twenty-dollar note was created in 1966.
Twenty Australian dollars
The Australian Twenty Dollar note is mostly red (with black, grey and white).
The Reserve Bank of Australia advises that there are approximately 132,600,000 Australian Twenty Dollar notes in circulation as at 30th of June, 2009.
The first Australian Twenty Dollar notes, along with the One, Two and Ten Dollar notes, were issued on the 14th of February, 1966 for the introduction of Australia's new decimal currency.
There are many possible types of misprints. Please post a new and separate question that describes the misprint.
cheak on Museum of Australian Currency Notes
Mary Reibey and John Flynn.
The Australian Koala series of coins were only ever minted in platinum and the Twenty-Five Dollar coin was only ever issued as part of a set.
The Royal Australian Mint never issued a Twenty Dollar coin until the 1990's and then usually in a mint set of bullion coins.
Australia puts famous or historically significant Australian identities on its banknotes. The original paper Australian Twenty Dollar note (1966-1993) had Sir Charles Kingsford Smith (aviator) on the front and Lawrence Hargrave (aeronautical pioneer) is on the reverse. The current polymer Australian Twenty Dollar note (1994-present) has Mary Reibey (ex-convict & pioneer business woman) on the front and Rev John Flynn (pioneer of world's first aerial medical service) is on the reverse.
The first Australian One Dollar note along with the Two, Ten and Twenty Dollar notes, were issued on the 14th of February, 1966, at Australia's conversion to decimal currency. The first Australian One Dollar coin was issued in 1984.