As per the Hanafi school of Fiqh, Qunut is Wajib (compulsory) in Witr. In the 3rd Raka'at, after finishing the recitation of Surah Fatiha and another Surah after it, the Takbir should be said, the hands should be raised to the ears and again bound and then the Qunut should be recited. After this the Ruku should be done. As given in Fatawa A'alamgiri, Kitab Us Salaat, Vol. 1, Pg No. 111).
In the opinion of Imam Shaf’aee, reciting Qunut in the last Raka'at of Witr in the last half of Ramadhan is a Sunnah, as given in Al Fiqh Alal Madhahib Al 'Arba, Vol. 1, Pg No. 307.
Do we have to raise hands before reciting Dua Qunoot in Salaat Ul Witr
It is Compulsory (Wajib) to say the Takbeer (i.e. say Allahu Akbar) in Salaat before reciting Dua Qunut and it is a Sunnah to raise hands when saying the Takbir. There is a Hadith in Musannaf Ibn Abi Shaiba:
Translation: When Hadhrat ‘Abdullah bin Mas’ud (May Allah be well pleased with him) would complete the recitation of the Holy Quran (in Salaat Ul Witr), he would say the Takbeer and then recite Dua Qunut. In another, it is clarified that he would raise his hands up to his ears when saying the Takbeer for Qunut. (Musannaf Ibn Abi Shaiba, Vol. 2, Pg. No. 206)
‘Allama Ibn A’abideen Shami (May Allah shower His mercy on him) has clarified that it is Compulsory (Wajib) to say the Takbeer and it is a Sunnah to raise the hands when saying the Takbeer. As given in Radd Ul Muhtaar under Waajibaat Us Salaat and under the details of Salaat Ul Witr.
What if don’t remember Dua Qunoot
If someone doesn’t remember Dua Qunoot, for the time being, that person can recite, “Rabbana Aatina Fid Dunya………………..” or can recite, “Allahmaghfirlee” thrice or recite, “Ya Rabee” thrice and should memorize Dua Qunoot as soon as possible.
What if forget to recite Dua Qunoot
If someone forgets Dua-e-Qunoot and performs Ruku’, completes the Salaat in the proper order and performed the Prostration of Forgetfulness (Sajdah Sahw) in the last sitting of the Salaat, then according to the Shariah, the Salaat is done.
It is a rule in the Shariah that if one performs the Ruku’ without reciting the Dua Qunoot, then as the occasion for reciting the Qunoot has passed, the person should not return to the standing position (Qiyam) for reciting the Qunoot. Instead the Salaat should be continued and Sajdah Sahw should be performed. As given in Durre Mukhtar, Vol.1 Kitab Us Salaat, Pg. No. 495.