I don't happen to have the PC game files, so I'll be using the Rules of Survival Android release (latest, of course).
Alright, here we go:
First, I grabbed the .apk file and .obb file from one of my devices and extracted both using 7-Zip. Taking a quick look at the extracted .apk, it seems like there's not much of interest.
So, we'll move onto the extracted .obb file.
Immediately you'll notice some larger files with .npk extensions. Looking at them in a hex editor (I use
HxD), we can also see that they have a "NXPK" header.
A quick Google search turns up a
QuickBMS script by aluigi (found
here) which can extract from these files.
So, I went ahead and extracted "character.npk" with the script and looked at what files I had now.
Most seem to have a .dat extension, but looking at them in the hex editor again we can see some use a "KTX 11" header, while others use an unreadable header (which I assumed to be models, and was correct).
I did a little bit more digging and found a model viewer and exporter for those strangely-headed files called
RMA Viewer, and was able to extract the KTX .dat files with
Mali Texture Compression Tool (I had to rename the KTX .dat files to have a .ktx extension for the Mali tool to recognize them).
From there, you can assemble your textured models and there you go!
Hope this helps, cheers!