The RAW files are saved in the same location as where your phone stores jpegs - usually in the DCIM/Camera folder on your main storage, or the dedicated location on your SD Card (Camera is usually the folder on LG Phones). They are saved with the .DNG extension (Digital Negative). The LG G5 takes both a Jpeg and a RAW at the same time when shooting in manual mode.
Open Snapseed, and navigate to that folder and you will have both the RAW photo and the JPEG next to each other. The first time you tap a RAW photo, Snapseed will tell you that it supports RAW photos and that all RAW processing features will automatically be available. Once you say OK, Snapseed will add a watermark in the bottom left that says "RAW" so you know when you are processing RAW photos (in case the extra RAW features aren't enough to make you aware).
That's it.