Whirlpool top-loader LSQ9200LQ0 The top half of the agitator is not turning. I am assuming it is a stripped part. What would be the best way to take this apart??

Pop off the cap.take off water proof cap,it has rubber seal.loosen nut.lift top half off.replace,agitator dogs.put it together in reverse.

You have what bad "agitator dogs". Yes this is a stripped out part. To get to the dogs, you will need to take the fabric softener dispenser off the top of the agitator (if your unit does not have a dispenser, then just take the cover of the agitator). Under that you will see a semi transparent cap that fits inside the shaft of the agitator, pull that straight up and out of the agitator. Now you can see the bolt that hold the agitator to the transmission shaft, this is a 1/2" or 9/16" bolt. You will need a socket with a long extension to reach this. Take a digital picture, or sketch the position of the dogs inside the agitator, this will help with the reassembly process. Once the bolt is out, the agitator will lift off. Turn the agitator upside down and depress the tabs up inside the shaft of the agitator, this will release the top of the agitator from the bottom, be careful, there are small parts that will fall out. Try to separate it in one piece, as this will make it easier to reassemble. Once separated, remove the old dogs and replace with the new, reassemble in reverse. When tightening the bolt, only tighten snug, the black rubber gasket should not bulge out when tightened. Also make sure the "o" ring on the semi transparent cover is in place and not broken. If you have questions, write me back. Hope this helps!