How many museum ships from World War 2 are carriers?

Four that I'm aware of, all American.

The USS Yorktown (CV-10) at Patriots' Point in Charleston Harbor, Charleston SC; The USS Intrepid (CV-11) in New York City; the USS Hornet (CV-12) at the former Naval Air Station in Alameda, CA; and the USS Lexington (CV-16) at Corpus Christi, TX.

The rest of the Essex Class carriers were all scrapped or scuttled. The USS Enterprise (CV-6), the only pre-war carrier to survive the war, and the ship that was in all the major battles, was also cut up for scrap.

The USS Midway (CV-41) is now a museum ship in San Diego, CA. She was commissioned nine days after Japan surrendered.