It depends on a lot of things, like the tuning, combustion chamber and piston top design, and air density and temperature. It's mostly engine design though. You're limited by detonation and pre-ignition, so if you can control that with the right air to fuel ratio and ignition timing, as well as a good knock sensor setup to retard timing, you can go pretty far. Ceramic coating the piston tops and combustion chambers can help too, and smoothing out everything with the slightest bit of an edge on it.. You're really trying as hard as you can to not make your spark ignited engine into a compression ignition engine (diesel engine). Running that high of a compression ratio means high cylinder pressure, and really fast changes in that pressure, so that's the enemy.
Speaking of that, stroke and other rod/crank geometry has an effect too, because that changes the expansion ratio (which is just the compression ratio on the other side of TDC, but is actually at least as important) and how fast the cylinder volume changes.

Motorcycle engines go over 12:1 on pump gas very easily, but that doesn't mean that the particular engine you have in mind will be able to do the same. Like I said, it's all about geometry and engine design.

So the answer is yes, you can do 12:1 compression, but it might not be easy, or cheap, and there isn't much safety margin for design and tuning if you're going to use pump gas. If you're looking to do something along those lines, I'd start with a lower compression build first, and do as much learning as possible with that, and then incrementally move up to higher compression. I really wouldn't recommend doing anything that high for a street build though; you're really walking on a knife edge for tuning and conditions, not to mention gas quality.