With a small telescope/binoculars, it will be difficult or impossible to resolve details on the scale of Io's disk (about 1 arcsecond). So you wouldn't be able to use shapes in the image to distinguish the two scenarios.
If you can attach a color filter, you might be able to distinguish between transit and occultation. Both Io and Jupiter are yellowish, so a color filter might not help much. But the other moons have more of a blue/grey color, especially compared to Jupiter. So a blue/green filter might make one of the other satellites appear to have a higher surface brightness than Jupiter, making it easier to see whether a transit is taking place.
Jupiter also has a big shadow. When it's far from opposition, a satellite may be in eclipse (invisible in the shadow) either before or after occultation (invisible behind the planet). Whether eclipse happens before or after occultation depends on the observing geometry. What it would look like is a satellite fading out early, before it reaches Jupiter's limb, or a satellite fading in at a position not quite touching the planet's limb.
Of course, eclipses never happen just before/after transits, so an eclipse is something that could potentially distinguish the two events.