There are three hidden items to be found on the Spy Academy map of Sniper Elite 5. This is a rather complex map to navigate at times, but so long as you take your time by systematically eliminating enemy forces as you move through it, you should be fine.
Where to Find Hidden Items in Mission 3: Spy Academy
Hidden Item - Kriegsmarine Playing Cards
This item can be found on a table inside the bar in the southwest of the map. The precise location is shown here.
Hidden Item - Covert OPS Field Manual
This item can be found on a table in the centre of the building where the spy academy set is located, in the northern part of the map. The precise location is shown here.
Hidden Item - Ornate Compass
This item can be found within the safe chest in the northwestern part of the building. You’ll need the “It’s Easy Money” intel to open it without a satchel charge. The precise location of the item can be seen here.