I have checked the shower head and it is clean. Removed the cartridge for cold water with water on and pressure is still very low. This led me to conclude cartridge and shower head are not the issue.

The cold water pressure is only low in this shower and is OK everywhere else. Also hot water pressure in this shower is fine as well.

How can I locate and dislodge debris for this line?

First you never remove the cartridge from the faucet when the water is still on, this could flood you before you could get to where you can cut the water off.

I am assuming this is a two handle faucet, because if you took the cartridge out of a single handle faucet, and the hot water is still on, you said it has pressure, you would have gotten a hot stream of water.

So turn the water off and take the cartridge out and look in the body of the faucet to see if you see anything in the hole in the back of the body of the faucet.

Can you post a picture of what you have or a model/brand. Some shower valves have an integral shut off built right into the valve body. Also are you certain there are no other stops on the line further back

John?? Fingers working funny today??

Sorry Bob yes it does, I don't like this change that they have done to this web sight lately, once again I am very very sory, Thanks.

Best Regards,
John

No sweat John, I can tell from your comment that you meant one thing but your finger gave you something else. Have a good one.