The vast majority or guitar input jacks are mono. You'd have to look at the positive pin or 2 pins inside the jack, and there is just one ground or sleeve connection.
I'm guessing that 99.9% are mono, knowing that some Gibsons, my Lucille and probably ES-345's or 355's, I dunno are stereo, and also some Rickenbackers with Ric-O-Sound Stereo - I have a 370-12.
So without being scientific, maybe 1 guitar in a thousand is a stereo guitar? Active, boosted and sustainer/sustaniac guitars, and basses might have a stereo jack for different reasons, because they either have 9V assisted pickups or a pre-amp/boost/sustainer. But acoustic guitars don't have a stereo jack, perhaps because the pickups are not active, so the pre-amp must be irrelevant, until your battery dies?
I'm not that familiar with acoustics, or don't care as much - we don't hot rod them.
Stereo cords, let's say 1/4" as an example are rarely seen, except with large headphones. You will note a small insulating ring between 2 positive ends, whereas mono cords have a negative pin, insulator and a single positive point to them. Stereo cords are what you get with Discmans and MP3's in much smaller versions, 1/8" or less.
Check your amp's specs, look for 2 inputs for L and R channels, which would also be extremely rare, because they are usually mono - maybe something can be done with effects loops and some of the other members might tell you.
Here's a good clear and open (not sealed or concealed) example of a stereo jack with a unique midboost Fat Tuesday!