Offbeats

@@bakawaka - I have never tracked my total grams of sugar per day, but I do eat a couple varieties of Greek (because it contains more protein) yogurt; Dannon Light & Fit and Oikos Triple Zero, both of which contain 7 grams of sugar. As @@toasty mentioned there are some sugars that are okay and I have also been told by my nutritionist that the sugar in yogurt is one of them. So, sorry I do not have an answer, but you should be able to find yogurt with less than 20 grams of sugar if you are concerned about that amount. Good luck!

My nut wants us not to have anything wtih more than 8g of sugar per serving. I break this 'rule' with my yogurt because there is only one brand/flavor i like. I try to avoid eating it daily. Otherwise I stick to it.

I don't know that I have ever heard anyone indicate the maximum grams of sugar per day. And I know that not all sugar is created equal, so to speak. Generally, sugar found in milk (lactose) is not as much of a problem as say table sugar or high fructose corn syrup, so I wouldn't worry about the sugar in Nonfat Greek yogurt. Other yogurts may have added sugar, though. Also, although fructose and sucrose can be a problem, in fruits with a high level of Fiber (such as apples, for example) the sugar is not really a problem.
So the answer seems complicated, and I don't really think there is a simple "no more than X grams of sugar" answer.
Generally, I follow the rule of very little ADDED sugar, or very little sugar from low-fiber products.