How many or which pages are required to be notarized to file a W7 for a person having H4 Visa and living in San Diego, California?
how can I obtain an ITIN ?

The W-7 is the application for an ITIN.

Photocopy ALL the pages of the passport. Considering that this can be done for 10 cents a page at Kinkos, Office Depot, Staples, Office max or any other office supply store, the costs is not that great.

In most states, the banks have notary publics who will notarize ALL of the pages you photocopied for free. Unfortunately, California has some strange law that prevents the notarization process. You may have to go to your country's local consulate office to have the photocopies certified as true copies.

chotu,
A couple of years I was in the same boat (trying to get a ITIN for my wife who was on H4). I sent a notarized copy of my wife's passport but the IRS kept sending bank letters of enquiry for stupid reasons: and each letter they send comes after about a month!

I am not saying that you should not send notarized copies but would like to suggest that you take the ITIN applicants original passport along with completed tax return to the local IRS office and let an official there make a copy of the passport, stamp the copies and submit the tax return there itself: somehow when the copies have a IRS officials stamp, things move a lot faster.

Going to a local office IS a better option, if the local office is equipped to handle ITIN applications.

Not all of the IRS office are so equipped. Call first and ask! It will save time!