Hi Pichico. Unfortunately, if the carto is not marked, there really is no way to tell if it's dual or single coil kind. Well, if it's a SmokTech XL carto and it's resistance is 1.5Ω, it's most likely a dual coil. Other than that, you'd have to take it apart.
Or you could try to figure it out by just
vaping it. If the carto is low resistance (like 1.5Ω) and produces a lot of vapor and not much heat, it's most likely dual coil. If it feels hot or starts to taste burnt, it's single coil. Since I don't know the resistance of your carto or the voltage of your battery, I can't give you any more specifics. Just enjoy it and when it goes bad (the flavor and vapor begin to diminish), take it apart!
Good luck.