What fasteners should I use to attach tongue and groove walls over drywall into foxblocks?

2.5" finish nailer will do the job .

I am guessing you don't know where the ties are in the foam. The drywall should be already fastened good. So I would just add glue between the drywall and wood panel and do what smartwall recommended.

Good Luck.

There is tie at every inside corner, coming out an inch, then every 8" on centre, until you get to where a common seam is.