ESAB CO2 regulator can i attach solenoid to this ?

Yes, you just need to find the necessary fittings and a solenoid that will fit.

One method would be to remove it so as to start w/ "most likely" NPT threads..but no guarantee.

Trick will b to figure out exactly what is there, what you can get to fit, ect.
Attaching a solenoid is easy, figuring out the fittings is not always so easy..

According to the spec sheet here:
Buy ESAB Dura Series Double Stage Regulator ? Moxiesupply.com

3/8BSP outlet r/h thread male
0.860 x14TPI R/H female..inlet from CO2

Plenty of cheap hot ones out there..