This thread goes over a similar question regarding the IQ Panel 2
Note that unlike the original IQ panel, the IQ Panel 2 siren output is just a relay, it does not produce voltage itself. The ENB terminal is looking for a voltage trigger.
This is not a big deal and still just requires two conductors run to the panel, as you can use the aux output on the hardwire 16 as the power supply to trigger the ENB.
On the IQ Panel 2, wire the two terminals to ENB and the first AUX. This will deliver voltage to ENB when siren is engaged as GNDs on the Hardwire 16 are all connected already.
You would then need a jumper between the second AUX and IN. Wire the siren + to OUT and the siren - to GND.