Sometime when using quotation marks at the end of a sentence or phrase, it would seem that two punctuation marks are required (one for the quote and one for the sentence).

However, you only ever use one punctuation mark, whether it is a full stop, exclamation mark, question mark, or anything else, at the end of a sentence.

In order to know which one to use, consider which is more powerful and use that one.

Some examples:

The teacher yelled out ‘Quiet!’
Did you say ‘John will fix my car’?
Someone might wonder ‘why did he choose that colour?’