What sort of Punto is it ?
IIRC when i did the Head Gasket on mine i found it behind one of the plastic Timing belt covers, at the front of the engine, RH side, very close to where the cylinder head connects to the main block. I seem to remember that it was quite hard to see even with all of my engine in bits.
You may find a simple barcode sticker on the timing belt cover with the same details on. Basically you'll just ahve to look hard.