What does this symbol mean on a schematic (like an audio jack with a zigzag line inside)?
It's a test point connection, usually runs to a pad (or other connector) on the PCB you can connect a measuring device to. The designator "TP#" (Test Point) is a common abbreviation.

Edit: from comments (brhans) the zig-zig on the pin may suggest it's a pad designed to accept a spring loaded pogo pin on a test unit.