Mr Google gives 6g carbohydrate per 100 ml for soya milk, 58 g carbohydrate per 100 g for cacao and zilch for the canderel. So a 300ml cup with 10g of cacao would give about 24g carbohydrate - 18g from the soya milk and 6 from the cacao. For some that would be a lot for one drink, for others it would not.
As has been said there is only one way to find out what it would do for you but if you are not blood glucose testing then you will not be able to find out by a simple test. Are you keeping a food diary? If so then maybe you could set a daily target for total carb intake and aim to keep to that.
What to aim for is a good question. One approach would be to sit in a quiet corner and write down everything, yes everything, you ate over the last week - including biscuits with your tea.. Do a bit of weighing to get an idea of what 100g of stuff looks like. Most carbohydrate contents are give in g/100g, and you need to know what 100g looks like so that you can get an idea how much carb there is in your portion sizes. Use your book and google and info labels on packets to estimate how many grams of carbohydrate you ate in each meal and snack and add it all up to give you how much you ate each day. No need for great precision, good idea would be good enough. Its not as hard as it sounds because we tend to be creatures of habit and when you have worked out the carb content of a meal, or cake or biscuit you can use that value next time. When you have done that pick a number that is lower than what you are currently consuming and work to that as your target. This time you work out the carb content before you start planning your meal and either eliminate something or reduce portion size to hit somewhere near your target. Build in a bit of slack and bingo, you can have you soya/cacao drink without worrying. You don't need to hit the bullseye every time, keeping the darts on the board will be good enough.
For me, I control to about 80 g carbs a day compared to probably 150-200 g when my blood glucose went from OK to not OK very quickly. It is now OK. Others aim for lower carb intake and others aim higher. Keep an eye on the bathroom scales. If your target is working for you, then you are likely loose some weight almost without noticing it. Rethink if you loose.a lot of weight quickly especially if you are currently at a "healthy" weight.
Hope that helps, it's one persons perspective on the issue.
