This 'Placebook' of JND is held in the archive of the PBCC. Not much is known about it, though it originates from his days at Trinity, but I understand it  contains notes from his university years, and was used later in life also to make notes and comments on a range of subjects.

Here is a picture of the book (used under fair-use copyright provision but acknowledged to be copyright to UBT);

[This post has been edited from the original at the request of Peter (see below).]

I know many PBCC members have registered on this website over the years, and some I think might be regular users - so I wonder if any of them reading this might be generous enough to provide us all with some more information on this item, or if they were especially nice to let me have a look at it :)