First thing you need to know about Shadow Warrior 2 is how this game generates levels.
There are some levels set that will always be the same but majority of the game is procedurally generated. It means those levels are random so if you can't find a secret I'm showing in this guide don't worry, there are different missions played in the same area like Shadow Hills so play the game and maybe you'll get missing secrets later.
You can also jump from one finished mission to another hoping to get new tiles and secrets.

When looking at my guides pay extra attention to the map and try to find identical spot in your game.
Many tiles, from which levels are built, are very similar so pay attention to details.

https://www.youtube.com/watch?v=nXng2Zalh0Y&list=PL6gLdnVOCnjXs2RF1ZW6di5ZH7JzXUcGy&index=23

12 secrets in one video!