Answered by Shaykh Faraz Rabbani
Is taking notes while listening to the khutba permitted?
Walaikum assalam wa rahmatullah,
I pray this finds you in the best of health and spirits.
The principle is that everything disliked or impermissible in prayer is disliked or impermissible during the Friday sermon (khutba), because the khutba is akin to half the performance of the Friday prayer. [Sarakhsi, al-Mabsut; Shurunbulali, Maraqi al-Falah; Ibn Abidin, Radd al-Muhtar]
Thus, taking notes during the khutba would be impermissible. One can, however, record the khutba and take notes later.
And Allah alone gives success.