Adjust the settings below to automatically generate a command. Once you've got everything right, hit the Copy button and paste it into the console in CS:GO.
This command would play the file exampledemo.dem (.dem part isn't needed). The file would be placed at Steam\steamapps\common\Counter-Strike Global Offensive\csgo\exampledemo.dem
The demo file for this command would be placed at Steam\steamapps\common\Counter-Strike Global Offensive\csgo*replays**\exampledemo.dem