I'm doing a presentation on Tor. Is it possible to capture and find keys and decrypt data.
If you're doing something like a presentation, paper, book, etc, it's best to 1. Ask the developers and contributors directly https://www.torproject.org/contact/ and 2. Read the documentation for yourself.
So, you open the Tor browser and connect to your favorite website anonymously. Tor Browser reaches out to a guard node. The guard sends the browser its public keys. The packets are then encrypted with those keys and sends them off to the guard which then then sends them to the next node, etc.
The browser does not ever get to see any private keys and so there are none to be found.
See also these links:
Theft Of Tor Relay Private Keys? (scroll down to find the section)