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.
Attending the gatherings of Thikr (i.e. Remembering Allaah The Almighty) and listening to preaching are among the acts of worship. Many evidences were reported regarding the virtue of that and encouraging it. However, we do not know of any specific evidence regarding the legislation of sermons during the nights of Ramadan. But it is something included in the general evidence that supports the great status and honor of attending the gatherings of Thikr. For more benefit, please refer to Fatwa 88049.
Standing on the pulpit in other than Friday prayer is something permissible and there is nothing wrong with it for the Prophet, sallallaahu ‘alayhi wa sallam, used to do that. One of the proofs of that is that Anas ibn Maalik said: "The Messenger of Allaah, sallallaahu ‘alayhi wa sallam, came out as the sun declined at mid-day and offered the Thuhr prayer. He then stood on the pulpit and spoke about the Hour (Day of Judgment)." [Muslim]
As for asking questions of the gathering, then it is something permissible in principle. It is one of the methods that the Prophet, sallallaahu ‘alayhi wa sallam, used in teaching his companions. It was reported by Al-Bukhari and Muslim on the authority of Ibn ‘Umar that: "The Prophet, sallallaahu ‘alayhi wa sallam, said: 'Amongst the trees, there is a tree, the leaves of which do not fall and is like a Muslim. Tell me the name of that tree.' Everybody started thinking about the trees of the desert; and I thought of the date-palm tree but felt shy to answer; the others then asked, 'What is that tree, O Messenger of Allaah?' He replied, 'It is the date-palm tree.'"
Al-Bukhari included this Hadeeth in a chapter entitled "The Imaam asks his companions to test their knowledge."
However, mocking and laughing at the answers of the gathering is something denounced. It is also a reason for making people dislike good deeds and turning them away from benefiting from such gatherings. Hence, laughing at the answers of the gathering or mocking their falling asleep (in the mosque) or the like should be stopped.
On the other hand, cracking jokes and laughing in the mosque or on the pulpit is something permissible in principle if the used words are lawful and decent. The Companions would talk about matters pertaining to Jaahiliyyah (the pre-Islamic period of ignorance), and they would laugh while the Prophet, sallallaahu ‘alayhi wa sallam, would only smile. [Muslim]
However, we do not know that telling jokes during sermons or lessons is part of the guidance of the Prophet, sallallaahu ‘alayhi wa sallam. For more benefit, please refer to fatwa 87027.
As for asking the gathering to take oath to renounce sins, then it was not reported that the Prophet, sallallaahu ‘alayhi wa sallam, did that with his companions and thus one should stop doing that. Anyway, the gathering's answer to him saying: 'Allaah Willing' is not an oath; so they do not have to make expiation for it.
Allaah Knows best.