The 1756-ENBT an "A-B" module, from the Allen-Bradley brand made by Rockwell Automation. "ABB" is ASEA-Brown-Boveri, a larger Swiss company that also makes control systems.
Can you describe exactly what information you are looking for, and why ?
Are you asking about the number of buffers on the backplane ? Or the size of an unsolicited message that the module can handle ? Or the maximum size of an I/O connection over EtherNet/IP protocol ?
Any of those things might be considered a "buffer size".