There is no way to know this with a 100% accuracy. Because when you look from outside, a trader moving Bitcoins between exchanges is no different from someone paying for a services/goods with Bitcoins. Both are Bitcoin transactions. The same goes for people moving money internationally, sending their parents Bitcoins, a company paying it's employees etc. You really can't separate these from purchases of actual goods and services. Because like I said, they're all transactions.
However, if you want to measure speculative interest in Bitcoin vs. interest in Bitcoin as a currency(i.e for practical things) then you can look at this graph:
And the discussion about it:
Both the discussion and the data is quite far from conclusive though.