Erlang knowledge is not a requirement to start learning Elixir. You will end up learning about Erlang programming model anyway because Elixir builds on top of it.

By "programming model" I mean things like immutability, concurrency, fault-tolerance, and the way you design systems with OTP.

You should be able to jump straight into Elixir. If anything, Elixir is probably a reasonable gateway into learning Erlang.

Disclaimer: I studied Erlang before Elixir, so I don't have a fresh perspective.