I posted what is below, but rereading your question, I think you are only looking for the demo file location? You should find it here.
C:\Users\[User name]\ AppData\Local\Activision\CoDWaW\players\demos
Recording a demo
Bring up the console (~) in game.
Type /record followed by the name of the filename you want to record the demo to:
e.g.
/record xyz1
Type /stoprecord if you want to stop the demo.
You can then /record another demo - or overwrite the file you just stopped.
Playing back a demo
Typing /demo will give you a list of demos you have just recorded.
/demo xyz1 will play back the xyz1 demo.
You can also play back demos with the Demo player found in the XI Downloads section. https://www.xtremeidiots.com/files/category/31-demo-manager/
Alternative, if you have a Nivida card, you can record with GeForce Experience. Demos however, are best for the uses of monitoring and scrutiny.