I am assuming your doctor told you to restrict potassium in your diet? Not everyone with kidney disease needs to restrict potassium. For people in pre-dialysis stages of CKD there is no benefit to restricting potassium (and may in fact be disadvantages) unless your levels are testing high. If you do need to restrict potassium, your doctor should tell you how much potassium you should have each day to keep your potassium level in the healthy range and what foods/medications/etc contain high levels of potassium. However people on hemodialysis do generally need to limit potassium intake in order to avoid too much build-up between treatments. With peritoneal dialysis, one may be able to have a higher potassium intake but check with your doctor to be sure. You might already know all this but I thought I'd mention it in case you didn't or in case anyone else with kidney issues is reading this post and assumes that they should be avoiding potassium.
As for gynostemma, I know it is used in Chinese Medicine to help the kidneys, but would recommend using it under the supervision of a herbalist or other health care practitioner knowledgeable about it's use. Animal tests have shown gynostemma overdose can lead to kidney failure, so I would recommend using it with someone experienced to guide you and monitor you for any side effects.
Gynostemma does contain some potassium, as do almost all plants and foods. But as far as I know it is not high in potassium, and even if it were it is normally taken in small amounts. Please ask a herbalist or naturopath to be sure if it is safe for you to take.
