All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
Giving religious lessons is a good thing to do at any time. This applies whether it is done before or after the speech of Jumu‘ah (Friday's Congregational Prayer) or any other time, as long as it does not disturb those who are praying.
However, if the lesson is held then only because it is Friday, then this is not permissible because neither the Prophet, sallallaahu ‘alayhi wa sallam, his companions nor our righteous predecessors did so. Dedicating a specific time to a certain act of worship requires supporting text from the Quran or the Prophetic Sunnah.
Allaah Knows best.