It has 2 plugs NGK D9EA
There are two, you will need to remove the tank to reach them on top of the cylinder head cover.
I'm guessing the same as most other bikes... under the gas tank. take a look at this video http://www.youtube.com/watch?v=Ct31s5JNhyM The spark plugs are located under the gas tank and under the...
two = )
NGK recommend NGK CR9E with a gap of 0.7mm (alternatively use NGK CR9EIX - iridium electrode for better spark)
NGK recommend 0.7mm. For further assistance contact www.aprilia-merseyside.com