بسم الله الرحمن الرحيم
The 4 rakah sunnah of Jumuah should be offered before the khutbah of Jumuah. You should reach the mosque at a time that you may offer the sunnah of Jumuah. In case you cannot offer it before the Jumuah salah you may offer it after Jumuah salah.
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.