If you would like to jog but your joints are not responding well, you should make an appointment with your doctor or a physical therapist to determine if there are any medical reasons for your knee pain. If you have clearance to exercise, you certainly could try hiking or walking on a treadmill with a little bit of an incline to add challenge. These activities involve less impact for your knees. You can further improve your aerobic engine, without incurring the shock of jogging, by walking or hiking faster. You dont necessarily have to start race-walking, but picking up the pace can provide a training effect very similar to jogging, and alleviate a lot of knee issues.
As with any activity, if you are just starting out, begin slowly and as your body adapts to the effort, you can add more time to your workout, more days per week, or a harder intensity (such as adding a little more incline to the treadmill). You may find that as your body adapts to the challenge of the activity and your legs get stronger, your knees may improve. After spending a few weeks gradually getting your body used to exercise, you could try adding a little bit of jogging (i.e. one minute of jogging to 5 minutes of brisk walking) and see how your knees tolerate that.
There are also plenty of strengthening exercises you could do to start to strengthen your knees. Mini-squats (just dropping about ¼ of the way to the ground rather than the big squats the body builders do) can be very effective, although if you have any questions about how to perform them you should seek help from a trainer. Another great exercise is wall squats: stand against a wall, then slide your back down the wall so that your knees are bent at a 90 degree angle, like you are sitting on a chair. Start out by doing 3 sets of these for 10 seconds, and as your body gets stronger you can add more sets or more time.
Another great exercise to consider if your knees dont allow you to run is cycling; a good bike ride is a great way to burn calories, build leg strength, and improve cardiovascular fitness, and you dont have the impact to your joints that some people find troubling with running.