Also, I wouldn't get hung up on it too much. It'll come as you gain experience. In the meantime, if you are buying 1ounce coins/rounds (eg ASE, buffalos) or 10 ounce bars from reputable dealers or from folks here, you can assume that they are talking troy ounces. Look at an ASE and it just says 1 oz - but it means 1 troy ounce as that is a standard weight system for au/ag.
But if you are not sure ask. No one should think any less of you for making sure. The only stupid question is the one you don't ask.