Jupiter is now prominently on display for amateur astronomers. A telescope of 2 inch aperture will show the main cloud bands along with the planet's four Galilean Moons. However, for useful work a reflector of 6 inch aperture is the minimum size that will allow you to begin making transit timings of the cloud features as they cross the planet’s central meridian.
The planet spins rapidly in 9h 50m at the equator so cloud features can be seen transiting the central meridian twice a day, although at around opposition one of these timings will occur in daylight when Jupiter is below the observer’s horizon.
Undoubtedly the feature that most amateurs want to see is the Great Red Spot, a 75mm (3 inch refractor) or a 15 Cm (6 inch) reflector will show it, while telescopes of larger aperture are ideal.
The Great Red Spot lies in the south Equatorial belt, however, do bear in mind that astronomical telescopes turn the image of the planet (and everything else), upside down, so that the GRS will be seen in the upper of the two Equatorial cloud bands as seen through the eyepiece. The photo here is right-side-up.
The longitude of the Great Red Spot changes steadily over time, and as the most recent data shows it is presently centred on 240°. This allows us to predict the dates & times when the GRS is best seen as it transits across the planet’s meridian.
Here are the most recent Times when the GRS will be on view, as an exercise, see if you can observe the Great Red Spot on the next clear evening.
Click on the graphics to enlarge