Sasuke was trying to read Sarada's memories

[shelke]

Reading memories with Sharingan does not kill anyone. Sasuke has done it more than once in the manga. Obito as well.

Probably.

 

[Berserker]

Correction OP: Sasuke could've genjutsu'd her memories but didn't because he realized that was his daughter.

 

[JStar King]

Where does it say that?

Human Path means that he was going to yank her soul from her body. It was stated that this will kill the intended target instantly.

The Human Path (人間道, Ningendō) grants a Rinnegan user the ability to read the mind of any target by placing his hand on the target's head or chest and yanking the soul out of the body. Though it provides intel by getting well guarded secrets, the technique inevitably kills the target. In life, Nagato channelled the powers of the Human Path through the corpse of a Takigakure shinobi.

In battle, the Human Path is relatively worthless compared to the other Paths as Nagato was quick to sacrifice it to protect the Animal Path against his final battle in life against Naruto.