Answered by Sayyidi Habib Umar bin Hafiz (may Allah protect him and benefit us by him).
What should we do on the night of the Isra’ and Mi`raj?
Nothing specific is prescribed on that night. However, if you hold a gathering, you should talk about the Prophet ﷺ and the Mi`raj and pray for the Ummah in abundance. Fasting on the following day (27th Rajab) is also good. Rewards for doing so are mentioned in some narrations. Although these narrations are weak, fasting is generally recommended in the sacred months, of which Rajab is one.