If you're thinking this will be a long guide along with a long process, it is best not to continue any further because this guide is gonna be a long long one.
The game has a complicated system (sorry english is bad.) for mods. I'll explain it later.

1. Post of Mark Mursaki - Audio Director of Tripwire Interactive for Killing Floor 2 Sound Mod
You can get the compiled folder of Mark in the link he provided.

2. Download Wwise v2015.1.9 build 5624 (64-bit) Version (don't go for the latest or below for compatibility) on their website, Audiokinetic.
Also, IF YOU ARE PLANNING TO DO A FULL VOICE MOD PACKAGE FOR A CHARACTER, try to register for a free registered-account (no payment required and give them your information) since a free non-registered account will only limit your Wwise soundbank(which is your output compiled in one file) to 200 sound files only. Any more beyond that and the Wwise program won't let you export the sound package. I manage to register for a free account for a limited time only like 3 to 4 months.

3. Download Audacity (it is a free sound editor and I'm currently using it for my sound files on Wwise etc.)

4. Get your sound files ready for your character.

5. Folder Shortcuts depend on your preference (for fast access since you have to tunnel for other locations)

Part 1 - Getting to know what to do

Part 2 - The Long Process

Part 3 - Final Part of the Project and Converting (Test Video)

I would like to give thanks and a round of applause to the people who have helped me with the WWise program and what to do.
Shout out to F O X (he's one of the skin modders on KF2 and primarily helped me on what to do here), to Mr. Mark from Tripwire for giving me tips and answering my questions, once again THANK YOU for the compiled project, and lastly to other modders in the KF community for giving me info and tips for the project. you know who you are guys xd

And to the people who liked my mods even though some may not like this type-of-content, thank you and hope more people can bring good quality content into the community as well.

Have a Nice Day!