The "Diamond" exoskeleton is the best in the game in terms of its characteristics. Previously, it could be found right after the beginning of the game at Yanov, on the roof of the "Iskra" bunker. However, with later patches, it was removed from there and now lies inside the bunker, where it cannot be reached until the story progresses to the moment when the bunker is unlocked.

So where can you find it now? The answer is simple: our path leads to Pripyat (I’ve described in detail how to get there in another of my guides).

Once we’ve reached Pripyat, we need to head to the "Sonechko" kindergarten (but before that, it would be a good idea to arm yourself well and get at least a decent suit of armor).

When we’ve reached the point marked on the map, we need to take the stairs to the second floor. As a landmark, you can use the bloody inscription on the wall nearby.

Run to the stairs and go up, but be careful — it’s full of Monolith fighters there, and they’ll shoot at you with everything they’ve got.

Approach the passage and head into the room as shown in the screenshot.

Enter the room with the Monolith antenna, where the "Diamond" exoskeleton will be located.
Grab it and get out of there. By the way, you can upgrade it immediately in Pripyat at the "Energetik" PC with the local technician — install enhanced servos and you’ll be able to move freely in the exoskeleton.

Sorry if I made any mistakes, English is not my native language.
Thank you for reading my guide! Good hunting, stalkers!