When Is Laylat al-Qadr?
Question

When is Laylat al-Qadr and how should we observe it? Is it by praying, or by reading Quran and the Prophet’s Sirah, listening to lectures and lessons and by celebrating it in the mosque?
Praise be to Allah.Striving hard in worship during the last ten days of Ramadan 
The Messenger of Allah (peace and blessings of Allah be upon him) used to strive hard in worship during the last ten days of Ramadan as he never did at any other time, praying, reading Quran and making du’a. Al-Bukhari and Muslim narrated from ‘Aishah (may Allah be pleased with her) that when the last ten days of Ramadan came, the Prophet (peace and blessings of Allah be upon him) would stay up at night and would wake his family up, and would abstain from marital relations. Ahmad and Muslim narrated that he used to strive hard in worship during the last ten days of Ramadan as he never did at any other time. 
How to observe Laylat al-Qadr
The Prophet (peace and blessings of Allah be upon him) enjoined staying up and praying on Laylat al-Qadr out of faith and in the hope of reward. It was narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings of Allah be upon him) said:  “Whoever stays up and prays on Laylat al-Qadr out of faith and in the hope of reward, his previous sins will be forgiven.” Agreed upon. This hadith indicates that it is prescribed to observe Laylat al-Qadr by spending the night in prayer. 
Du’a for Laylat al-Qadr
One of the best du’as that may be recited on Laylat al-Qadr is that which the Prophet (peace and blessings of Allah be upon him) taught to ‘Aishah (may Allah be pleased with her). Al-Tirmidhi narrated, and classed the report as sahih, that ‘Aishah said: “I said, ‘O Messenger of Allah, if I know which night is Laylat al-Qadr, what should I say on that night?’ He said, ‘Say: Allahumma innaka ‘afuwwun tuhibb al-‘afwa fa'fu ‘anni (O Allah, You are forgiving and You love forgiveness, so forgive me).” 
When is Laylat al-Qadr?
With regard to specifying which night of Ramadan is Laylat al-Qadr , this needs specific evidence, but the odd-numbered nights during the last ten nights are more likely than others, and the night of the twenty-seventh is the most likely to be Laylat al-Qadr, because that is mentioned in the ahadith. 
Can Muslims celebrate Laylat al-Qadr?
With regard to innovations, they are not permissible during Ramadan or at other times. It was proven that the Messenger of Allah (peace and blessings of Allah be upon him) said: “Whoever innovates anything in this matter of ours that is not part of it will have it rejected.” According to another report, “Whoever does any action that is not part of this matter of ours will have it rejected.” 
We know of no basis for the celebrations that are held during some nights of Ramadan. The best of guidance is the guidance of Muhammad (peace and blessings of Allah be upon him) and the worst of matters are those which are innovated (bid’ah). 
And Allah is the Source of strength. May Allah send blessings and peace upon our Prophet Muhammad and his family and Companions.