What are the type constants that the documentation for glGetProgramResourceiv() refers to?
For whatever reason, the text for that function documentation was copied from the GL_ARB_program_interface_query extension. Extensions in OpenGL are always defined relative to a specific version of the OpenGL specification. So if an extension references something in a specification, it's talking about that version of the spec.

However, the OpenGL specification was massively restructured between 4.2 and 4.3, with whole chapters moved around. This means that table references in 4.2 become completely wrong relative to 4.3 and above.

Program interface query was written against the 4.2 specification. Oddly enough, there is no table 2.16 in that spec; the correct number for that table is 2.13 (so it's likely a typo, since 3 is right below 6 on a number-pad). But even if the extension did mention the right table number, that table moved to a whole different chapter in 4.3+ versions. It's been renumbered and moved since then, so you'll have to look at a particular specification's definition of glGetProgramResourceiv to find it.

In general, if you find something incongruous in the documentation pages, you should look at the actual OpenGL specification to see what it says about the function's behavior. In this particular case, the docs in the OpenGL wiki for this function actually includes the table.