He might not be very familiar with what goes on in a modern synagogue, but he’d be more familiar with it than he would with anything happening in any church anywhere.
Except the Eucharist, of course. Assuming we can accept the story of The Last Supper as being more or less historically accurate. But yeah, most Christian Churches (I assume you mean “Christian”) hold services in the vernacular, and Jesus wold be unfamiliar with most of those languages (except English, of course 
). The sermon might also be familiar since he was famous for giving a few himself, and there is generally at least one reading from the NT, which if we again assume to be more or less historically accurate he might say: I yeah, I remember that!
Now, if we assume that Jesus is God, and all-knowing then the whole language issue becomes moot. In fact, it all becomes moot, because well, “all knowing”. But if we assume he was a man of his times, transported to present day, then all bets are off on that front.
In a Catholic mass, there’s typically one reading each from the Gospels, the New Testament other than Gospels, and the Old Testament. So assuming we can get past the language issue, he might say “I remember that!” to the Gospel, and recognize the Old Testament reading from his own scriptural studies (especially since the Old Testament passages most often read are the ones Jesus is recorded as having quoted). But the other New Testament reading would be from after his time on Earth. There’s also at least one Psalm (though of course, the precise wording of a translation of poetry will vary), and so he might recognize the words (but not the music) of that, too. And there’s also the Our Father prayer, which he ought to recognize at least in sentiment, even if he didn’t consider the precise words to be important.