How do you measure 100g of golden syrup?!
It's equal to a 1/3 cup approximately.
1 cup is approximately 360 grams so divided by 3 gives you 120 grams in each 1/3 cup or if you divided by 4, it gives you 90 grams in each 1/4 cup.
You decide - if you want a little more, use the 1/3 cup. if you want a little less then use the 1/4 cup.
pooterosa is correct.
And, measuring cups for liquids are marked in milliliters; since grams are a measure of weight, 100 ml on a measuring cup is not 100 g. It depends on the weight of the substance being measured.
turn the measure cup around and eyeball it from the side to see where the 100 mark is.