For most people, the simple answer is, "as much as you want". Please note the exceptions mentioned in article named "Are there any drug interactions I should be concerned about?". We recommend 4 to 8 cups per day of tea. If taking jiaogulan in capsule form the recommendation is usually 2 to 6 capsules twice daily.
I recommend taking a break from jiaogulan about every 6 months or so for about 2 weeks. There is no research supporting this, it's just based on my personal experience. Personally, I think our body simply becomes less sensitive to the benefits of jiaogulan when taken every day and a brief pause allows you to become sensitive again.