During salah in the last rakah I sit in Tawarruk position and recite Attahiyyaat and then I say the prescribed invocation (seek refuge with Allaah from four things). After that I want to pray for the good things of this world and the hereafter in my own language calling upon Allah by one of his names. During this period should my hands be kept in the same position as when praying Attahiyyaat (i.e My right hand index finger raised) or should the hands be held and raised together ?

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 ʻalayhi wa sallam, is His slave and Messenger.

The Sunnah includes raising the index finger during the Tashahhud, supplicating until the end of the Tashahhud and then concluding the prayer with Tasleem. It has been reported that Waa’il ibn Hajar said pertaining to the description of the Prophet's prayer, “Then, he, sallallaahu ʻalayhi wa sallam, raised his finger and I saw him moving it, supplicating with it.” [Ahmad and An-Nasaa’i - Al-Albaani graded it Saheeh (sound)]

Moreover, Ibn Baaz  said: “As for the index finger, the Sunnah includes raising it during the Tashahhud, from the beginning of the sitting until the Tasleem. It should be raised with a slight curve so as to point to the oneness of Allaah.” [Majmoo‘ Al-Fataawa]

Allaah Knows best.