The Prophet ﷺ taught Muslims to look for Laylat al-Qadr in the odd nights of the last ten nights of Ramadan (Sahih al-Bukhari 2017; Sahih Muslim 1169). He had been shown the night and was then made to forget it, so he told his companions to seek it in the odd nights of the last ten (Sahih al-Bukhari 2016).
Scholars have given different opinions about which night it is. Ubayy ibn Kab, may Allah be pleased with him, swore that it is the morning of the twenty-seventh, and said that its sign is that the sun rises on the following morning without strong rays (Sahih Muslim 762). Many Muslims therefore seek it especially on that night. Still, there is no fixed date that is agreed by all, and we should not claim one. Allah kept the exact night hidden, so that believers would worship with effort on many nights.
The best plan is to give your best effort in every night of the last ten, and especially the odd ones. When the last ten nights began, the Prophet ﷺ used to keep the night alive, wake his family and tighten his waist wrapper (Sahih Muslim 1174). The last ten nights begin at the sunset that ends the twentieth day, which is the twenty-first night. Because the Hijri month can start on different days in different places, follow the Ramadan dates of your local community.