Is raising the index finger when uttering the Shahada before death prescribed, and is there anything mentioned about it at all during the Tashahhud, or is it specific to certain situations like the Tashahhud after completing ablution?

The Sunnah indicates that saying "There is no god but Allah" at the time of death is one of the signs of a good ending. For this reason, it is legislated to prompt the dying person with the two testimonies (Shahadatayn), as the Prophet, peace and blessings be upon him, did with his uncle Abu Talib. Raising the index finger (pointing with the forefinger) is established in several instances, including: the Tashahhud in prayer, supplication (du'a), and when the Khatib (preacher) supplicates on Friday. However, there is no specific evidence reported for raising the index finger at the time of death, though it can signify the affirmation of Tawhid (monotheism), especially for someone unable to speak.