Hello

The answer from Mike is not correct. J1939-21 contains only the most basic messages.
The diagnostic messages are in J1939-73 which also are also few messages, but very important.
Quite a big amount of PGNs and SPNs is defined in J1939-71
But if you only purchase these it will still be incomplete.
This is only a small part of all the data that you will see on a real J1939 CAN bus.

The vast majority of J1939 messages is defined in the SAE J1939-DA.
It comes with a huge Excel file of 15 MB, which is even more important than the PDF's.
But not even this document contains all messages!

If you want to get an impression of the complexity of J1939 I recommend to install HUD ECU Hacker which comes with some example logfiles, like from real Heavy Duty Kenworth Truck.