You must use the secondary action key (default 'F' on PC) to place the book open on a surface. Tossing it with 'G' (drop) leaves it closed, and the ghost cannot write in a closed book.
If you witness a ghost event, try placing the book directly at the ghost's feet; they are highly likely to interact with nearby items immediately after an event. Fazmofobi
You can hear a distinct scratching sound when a ghost is writing, even from another room. You must use the secondary action key (default
Place a Video Camera facing the book. This allows you to check for writing from the safety of the van. Fazmofobi