It'* directly under the MAP sensor, which is on the drive belt side of the engine. There is a plastic twist-on housing that holds it in place and the MAP sensor mounts on top of that housing.
To test it, remove it from the engine and shake it, if it rattles easily it is good. If it doesn't rattle or if you have to shake it hard to rattle, it is bad. They are so cheap though, you would be better off to buy a new one and just replace it. Use GM only though for a PCV. It'* just not worth the dollar you'll save by going with aftermarket.
Make sure to get the 2 o-ring seals in the right location when reassembling the valve. If the o-rings don't seal properly it will cause high oil consumption, irratic idle and sometimes even a high pitch whistle noise from the engine.