There should be a file named pb2ents_b15.c on the pball2/entity/ folder.
pb2ents_b15.c is from build 15, not sure if Jitspoe is going to edit the entity list on the next DP BSP release.
The syntax of the entities is pretty simple:
/*QUAKED <ent name> (# # #)
help stuff in here.
*/
Not sure what the (# # #) means tho, and sometimes there are more than one parenthesis.
**********
EDIT:
Did a little research and...
The syntax is like this:
/*QUAKED <ent name> (color) (bounding box start) (bounding box end)? FLAGS
Help....
*/
(color) = color.
(bounding box start) = optional, start point of the bounding box.
(bounding box end) = optional, end point of the bounding box.
? = optional, Entity takes the exact size of the brush.
FLAGS = optional, Flags modifiers.
I could be wrong about the bounding boxes tho...