What does Parashara Smriti tell about Upanayana Samskara?
Parashara Smriti tells that all can have sacred thread ceremony (Upanayana).
Parashara Smriti is missing the Achara Kanda, that any Smriti must have. So, it does not say anything regarding the details of how the Upanayana ceremony should be performed. But it does talk about the sacred thread which is invested during the Upanayana ceremony.
- If, while performing the rite of Achamana, he has his Lead or throat wrapped with cloth, or the posterior hem of Lies under-garment is not tucked up, or his coronal lock is not tied, or if he is without his sacred thread, he remains impure, in spite of the ceremony of Achamana (from Chapter 12)
The text also talks about Dvija (twice born), who according to the other Smritis, are the only eligible persons for the Upanayana ceremony to be performed upon them.
- If a twice born, whether he leads a strictly religious life or not, is bitten by a dog, let a number of Brahmans be saluted by him, who render him pure by casting their eyes on him. (from Chapter 5)
So, the answers to your questions are: