It can be found by entering Old Gullet sinkhole and exiting on the other side. The Sole Survivor will exit from a basement into a house that is chained from the inside. It will be on the second floor in a chem cooler next to a mattress.
Sometimes the note will not be loaded, thus making it impossible to read. [verified]
- Reloading an earlier save or leaving the area and returning at a later time may fix the problem.
- Dropping the note, then reading (interacting with) it while it is on the floor, may also help.
- When picking it up, the note may behave the same as a legendary or quest item by capturing focus and playing that specific sound, yet the item can be dropped. However, it's not used in any quest or interaction. [verified]