Yes, a person with a height of 5'8" can generally ride and balance a KTM Duke 1290 R or other bikes with similar heights. The KTM Duke 1290 R has a seat height of approximately 33.5 inches (850 mm). While taller riders may find it easier to flat-foot the bike, a person of 5'8" height should be able to handle the bike comfortably.
It's important to note that rider height is just one factor to consider when determining if a bike is suitable. Factors such as leg inseam, riding experience, and personal preference also play a role. It's a good idea to visit a dealership or a motorcycle rental service to sit on the bike and get a feel for it. You can also try adjusting the suspension settings or considering aftermarket modifications like lowering kits to further customize the bike's height if needed.
Ultimately, rider comfort and confidence are key when riding any motorcycle. If you feel comfortable with the bike and are able to touch the ground with your feet while seated, you should be able to ride and balance it effectively.