What is the traditional day or congetional prayer for these religions: Judaism, Islam, and Christianity.
This is a good question. Let me answer in the order from which the religions came about in history.
Jews go to synagogue on Saturday. The reason for this is due to the creation order of Genesis 1 and 2. They have kept this pattern as long as one can remember.
Christians go to church on Sunday. They originally came together for corporate prayer and worship on Saturday, like the Jews, but the early church changed this due to the resurrection of Jesus. Their chief difference with the Jews is that they believe that Jesus is the messiah.
Muslims pray 5 times a day, but their most important corporate time of prayer is Friday.
These three Abrahamic religions all purport to worship the same God, but they tend to do so on different days.
To Muslims, the day for congregational prayer is Friday. Muslims go to attend services at mosques on that day.
To Jews, Saturday is the Sabbath. It is the traditional day to attend communal services and is also traditionally a day of rest that is treated much differently from other days of the week.
To most Christians, Sunday is the traditional day to attend church. This is not true for all Christians, as Seventh-Day Adventists, like Jews, observe the Sabbath on Saturday.