Spondylolisthesis is different from spondylosis. It is a condition where one vertebra "slips" forward over the adjacent vertebra. Spondy is Latin for "spine" and olisthesis means "slipping."
It is often at either the L4-5 leve or the L5-S1 level, which takes the brunt of the body's bending action.
I can tell you what exercises to avoid. You do not want to do activities that put your back in extension (in other worRAB, bending backward at the waist).
As with any back issue, it is important to keep your core muscles and pelvic floor and pelvic girdle muscles in shape, too. These all contribute to keeping your back strong and stable. Stability is the big problem with spondy...or, at least it can be. To this end, if you are able, you can do Pilates or yoga (but you have to avoid the twisting positions). You can swim, but you should avoid strokes where your back is in extension, such as breast stroke or actually any stroke done on your stomach unless you use a snorkle...otherwise it is hard on your spine. Biking can be good. Obviously, anything where you are lifting is out of the question. Running should be avoided as it jars the discs and will only make the situation worse. Actually any activity that involves a repetitive movement, bending, twisting or lifting, or any activity that involves a jarring motion such as skiing, snowboarding, riding roller coasters, etc. should be avoided.