The first time, take the job that is open, by solving the mixed paintings. Take the forgery detection course so you can get the key to the Supply Room. Go there and get the dragon face picture that is inside. Then you can exit the museum and sneak back in through the Underground that night.
(see related questions)
The art museum on counterfeit island opens after you go to the guy at the dock.
The Museum Fantastique is on Main Street, just left of the park where the blimp arrives on Counterfeit Island.
You go next to the museum and go to the balloon and leave.
after you get a job at the museum
In the museum.
it is on the top level in the middle of the museum.
At Early Poptropica Island
You have to get a job at the museum after you take the underground tour
it is at the museum on the top of the museum at..night.
Jump
in the museum of arts in counterfeit island
he is at the clown store