How do you pronounce word pseudonymous bosch?

You're likely referring to the author "Pseudonymous Bosch", which is a pseudonym (a fake name) used by an unknown author.

The pronunciation is:

* Soo-doh-nim-us Bosh

It's important to remember that the author's real identity is unknown. So, while the pseudonym sounds like a name, it's not necessarily a person's real name.