It is not necessary for all Jews to know Hebrew. There are different denominations of Judaism so - perhaps - if one was going to an orthodox or traditional synagogue, much of the service would be in Hebrew. If one went to a reformed synagogue, a lot of that service would be in English. There are also prayerbooks that provide the Hebrew, the English, and the transliteration of the Hebrew.
Many people can read the Hebrew but don't necessarily understand what they are saying without reading the accompanying English.