Documentation for the host server exit points is collected in the Information Center under the <a href="http://publib.boulder.ibm.com/infocenter/iseries/v5r4/index.jsp?topic=/rzaii/rzaiimst31.htm">Use server exit programs</a> topic.
Documentation for the TCP/IP servers is distributed across various topics, generally under each server area. For example, for FTP, the documentation is under the <a href="http://publib.boulder.ibm.com/infocenter/iseries/v5r4/index.jsp?topic=/rzaiq/rzaiqreferenceexit.htm">File Transfer Protocol exit programs</a> topic; and for the REXEC server, it's under the <a href="http://publib.boulder.ibm.com/infocenter/iseries/v5r4/index.jsp?topic=/rzal7/rzal7exitpt.htm">Exit points for controlling REXEC server</a> topic.
Those links are specific to V5R4, though specifications are generally backwards-compatible. Each release (and some PTFs) brings changes. Review of numerous PTF cover letters relating to specific servers can be necessary, depending on your intended usage and system history.
Many servers have no exit points. Some servers with exit points don't pass any useful info about the activity being done to the exit programs. New releases almost always bring issues, so access to "early release" versions of the OS might be critical if the exit programming itself is 'business critical' -- you can potentially shutdown access to your system if 'R'ejections are signaled incorrectly or open your system to the world if 'A'cceptance is signaled incorrectly.
Searches for information are usually best done by searching for specific exit point names. e.g., 'QIBM_QTMX_SERVER_REQ'.
That's about as far as I can go without a specific technical question to answer.
<b>Disclaimer:</b> I am employed by a vendor of exit point solutions for System i. Answers that I give will be as technically correct as I can make them, but I will need to be careful in how much and what kind of info the I supply.