"Dat zal jou niet helpen."
Translation:That will not help you.
How does one know whether this sentence means 'That will not help you,' or 'You will not help that'? Just down to the word order?
'You' in this sentence is the object, so it can only mean 'That will not help you'. In the sentence 'You will not help that.' 'you' is the subject rather than the object. The Dutch translation would be 'Jij zal dat niet helpen', which is a bit weird sentence in Dutch as we usually use "hem" or "haar" in these cases (because you cannot help stuff, only living things).
Nope, because 'dat' is the subject. So, the "you" in those sentences is the object: 'jou' (or the unstressed 'je') should be used. (So, yes, your second sentence is correct!) :)