First you will have to find out what Steam64 ID is connected to the account you want to spectate.

An easy way to do this is using the SteamIDfinder[steamidfinder.com]. Type in your steam account url or your custom url and hit "Find Steam ID".

A site like this one will appear.

Now you have to copy your steamID64 (Dec).
In this example the ID would be "76561197960287930".

In case you don't know how to download Wingman demos and where to put them, here is a good guide about it.

Now you should be able to view the demo via the command:

To watch a highlights video instead of the normal demo, simply add your Steam64 ID behind the name of the demo.

I am glad if the guide was helpful.

May you be blessed with clean games xD