I think you've answered this question already. 'Study', like many verbs, can be either transitive or intransitive. It's transitive in the first sentence and intransitive in the second. Note that 'everyday' is an adjective, though. As an adverb, it should be written as two words: 'John studies every day'.

Thank you very much for your explanation Peachy.

Just to re-word Su.Ki.'s answer (because this is very useful to remember), verbs don't divide equally into transitive *or* intransitive. Some can be both, and we know this by the presence of an object or not. You can always check a good dictionary, but usually the sentence in front of you will be enough.