I have seen in some mosques that they give Khutbas and speeches related to Islam on the night of Qadr. Is it correct or is it a Bid'ah? Please send me the answer of this question as soon as possible.

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Teaching knowledge in mosques is permissible.  The Sunnah is that the night of al-Qadr should be spent in performing prayers, making Dua and in Al-Ii'tikaf.  The Prophet (Sallallahu Alaihi wa Sallam) said: "Whoever established prayers on the night of Qadr, out of sincere faith, and hoping for a reward from Allah, then all his previous sins will be forgiven". [Reported by Imams Al-Bukhari and Muslim]

There is a Hadith that Ayisha (Radiya Allahu Anha) enquired the Prophet (Sallallahu Alaihi wa Sallam) about what she should say during the night of al-Qadr if she knew which night it was?  The Prophet (Sallallahu Alaihi wa Sallam) said to her to say: Allahumma Innaka Afuwwun Tuhibbu al-Afwa F’afu Anni (O Allah! You are forgiving and love forgiveness, so forgive me). [Ahmad, Al-Thirmidhi, Ibn Majah, Al-Hakim,Al-Arnawout and Al-Albani graded it Saheeh].

It is also proved in sound Ahadith that the Prophet (Sallallahu Alaihi wa Sallam) used to perform Ii'tikaf during the last days of Ramadan.

The Prophet (Sallallahu Alaihi wa Sallam) encouraged people to seek the night of al-Qadr in the last ten days of Ramadan.  He said: Look for the night of al-Qadr in the last ten nights of the month of Ramadan. [Reported by Imam Al-Bukhari].

Therefore, appointing a certain night as night of al Qadr is not correct as practiced in many countries.  It may be on the night of twenty first or twenty third, or twenty fifth or twenty seventh or twenty ninth since the Prophet (Sallallahu Alaihi wa Sallam) said: Look for the night of Al-Qadr in the odd nights of the last ten nights of the month of Ramadan."[Reported by Bukhari and Muslim]. The following is a general rule established by Shariah: It is considered an innovation (Bidah) in religion any act of worship that the prophet did not perform although the requirements of such act were present and there were no impediments that prevented the prophet from performing it.  

Allah knows best.