How do I get OMNI Level 1.0?

Have Hope follow the objective marker. You can locate the objective marker on the map by entering OMNI View and clicking the Map icon at the bottom.
If you do not see the objective marker, go to Settings, access the Gameplay tab, and turn the objective marker option ON.

Solve the puzzle in the Headmaster’s Dining Room and go through the fireplace. OMNI 1.0 is in the room to Hope’s left.