Molding question

Doing a silicone mold with Mold Max NV 14. Wondering if this should be a one or two piece mold.

That's never an easy question. It depends on how you are casting it.

Are you slush it with resin as a limited run?
Are you casting solid and production runs?

From the pics, if you were slushing, you could go one piece, fill the deep recesses and place the gate on top. The tapered design allows for easy removal and you'd only have to worry about bubble entrapment (if at all) in the bridge of the nose and lower teeth.

If you're casting solid, and want to keep the deep recesses, I'd go 2 or 3 piece depending on where your seem will be.

Best case scenario with sculpting is have your mold plan before you even start. A mold is the most important part of the whole process since it dictates everything. It save a lot of time redoing details and texture if you know going in where everything will be in terms of gates, vents and seems.

Resin casting and production. This sculpture is far from done, but I started thinking that the jaw might be a bit too much of an undercut for a solid one piece mold. The Mold Max is pretty forgiving but Im thinking ill go two piece on this.

2 or 3 piece would be the way to go then, you could pour from the bottom which would minimize cleanup. 3 piece would allow good seam placement.

I'd probable break it down into parts myself, the lower jaw and skull, that would give you the most options and allow beautiful deep areas in the mouth as well as avoiding bubble entrapment in the teeth. If you cast it as is, you're going to have to figure out some venting on the one set of teeth depending on how you pour.

The size of your model allows you to do a silicone BLOCK mold which would be the simplest way.