Assalamu Alaikum
1) When should we point our index finger in salah? Is it from the beginning of athahiyyath or while saying " lailaha illallah "?
2)what should we recite before tasleem in sujood sahv?
Jazakkallahu khairan

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Pointing with the index finger in Tashahhud is not obligatory in principle; rather, it is only desirable. The jurists differed in opinion about its time and whether one should point with the index finger throughout the Tashahhud or not.

Some of them said that the pointing is from the beginning of Tashahhud until the supplication at the end of Tashahhud and it is desirable to move the finger according to the view of the Maliki School.

The Shafi’i School is of the view that the pointing should be when saying ‘Illa Allah’. There are two well-known views in the Hanafi School as stated by Ibn ‘Abideen: The first: there is no pointing (with the finger), and the second: raising the index finger when saying La Ilaha (there is no god) and putting it down (lowering it) when affirming Illa Allah (except Allah).

The view of the Hanbali School is that he points with the index finger when uttering the Name of Allah without moving it; we hope that the matter in this regard is easy.

On the other hand, the worshiper should not recite anything from the Quran or glorification of Allah after the prostration of forgetfulness and before the Tasleem; nonetheless, some jurists are of the opinion that he should recite the Tashahhud after it and then say the Tasleem, for the Hadeeth of Imraan ibn Husayn who said, 'The Prophet, sallallahu ‘alayhi wa sallam, led them in prayer and he forgot (something), so he made two prostrations and then recited the Tashahhud and then made Tasleem.' [Abu Dawood, At-Tirmithi, and others]

Some reviewers of the Ahadeeth among the scholars ruled that the mention of Tashahhud in this Hadeeth [i.e. after the two prostrations of forgetfulness] is weak, among whom are Al-Bayhaqi, Ibn ‘Abdul-Barr, Ibn al-Munthir, Ibn Taymiyyah, and Al-Albani .

Others are of the view that the worshipper says the Tasleem after raising up from prostration [of forgetfulness] and does not recite the Tashahhud, because the Tashahhud is not proven after the Tasleem from the Prophet, the Prophet . We hope that the matter is easy in this regard, because even though the Tashahhud after the two prostrations for forgetfulness is not proven from the Prophet it was proven from some companions. Therefore, whoever says the Tashahhud after the two prostrations for forgetfulness, then there is no harm on him, and whoever does not say the Tashahhud (after the two prostrations for forgetfulness) and says the Tasleem, then there is also no harm on him.

For more benefit on Sujood as-Sahw (prostration for forgetfulness), please refer to Fatawa 333763, 404362, 370321, 89546 and 83932.

For more benefit on when to raise the index finger during the Tashahhud, please refer to Fatawa 91001, 92757, 119138, 276100, 276157, 293653, 326731 and 400048.

Allah knows best.