Connect two SQ6 sound consoles

How do you create aux’s on second SQ6 and connect thru FOH console to AR2412 AudioRack to control in-ear monitors

I don’t quite understand what you’re planning:
An additional monitor console (on stage), but the stagebox (also on stage) is connected to the FOH console (which would requiring two long CAT cables)?

Generally, you’ll need an SLink card to connect your three devices.
Within this system, you should then be able to patch all the necessary connections - also including an aux from the monitor console to the FOH console and from there back to the stagebox.

The two consoles need to be digitally connected (through SLink, Dante, Waves, Madi, etc). The stage box must also be connected to one of the consoles.

You will use tie lines (or direct outs) to send audio from the console without the stage box to the console with the stage box. The first step is to set up the routing on the console without the stage box and output whatever audio you want over tie lines (or direct outs). You can send channels and/or busses via tie lines. Second, you need to set the routing up on the console with the stage box to take that tie line input and send it to the appropriate stage box output.