A variegated leaf is a leaf which contains green and non green parts. As the green parts contain chlorophyll they can photosynthesise, but the non green parts do not contain chlorophyll so they cannot photosynthesise.
The easiest of these experiments is to place the leaf in boiling water for five minutes (to soften the cells and help the iodine soak in) and then in ethanol (alcohol) and when drained of colour spread out on a flat surface. Soak the leaf in iodine and the green parts will turn blue/black and the non green parts will stay the yellowish brown colour of iodine. The green parts contain starch (a more compact form of glucose) which makes iodine turn blue/black. The blue/black is what will show starch is present.