Well, this is South American Spanish and for me looks quite strange the sentence ( I'm from Spain) but I will give it a try. Si en buena onda = If in a cool way no te hagas la que no sabes nada del tema = don't pretend you don't know what I'm talking about (because I know you know what I'm talking) Di la neta de una vez por todas = tell the truth once and for all. I guess 'neta' in latin Spanish means 'truth'. In Spain we say ' verdad'

All these words belong to a language developed by Chilean "evil-doers" in the early 1800's. The language is called Coa (pretty much the same as Lunfardo in Buenos Aires). Many of these terms became popular and are now used by an increasing number of the population, particularly in Santiago. Though, many of the terms are used in a strongly offensive way (the sentence that you quoted is a perfect example of it) they can also be used in a friendly manner. But never in a formal context. If you just learning Spanish, I don't recommend to pay much attention to these terms since they can only be understood by Chileans (and not by all Chileans) and people who speak like that are not favourably viewed.

In a cool way (Si en buena onda) Don't act like you don't know about what we are talking about (no te hagas la que no sabes nada del tema) Say the truth once and for all (Di la neta de una vez por todas) In mexico those frases are common! :D

La neta = might be have many meanings depent of context, In this case neta means all or truth I am not Mexican but I born in Venezuela therefore I know their slang

Hello annat, this phrase means, the good way, don't pretent to tell me that you don't know anything, tell me the truth!! Or tell me it all!!