All the JTAG pins are available on J2. These are most easily accessible on a) a “connectors down” board plugged into a snickerdoodle baseboard containing the standard JTAG header (e.g. breakyBreaky, piSmasher) or b) a “connectors up” board.

Note: the “official” Xilinx JTAG-USB adaptor can be found here. Alternatively, some people have had luck with the JTAG-HS3 from Digilent.