1. If it's a Samsung (My Files is the name of their file manager, but other people have come out with file managers with the same name, so that doesn't tell us that it's a Samsung any more), the SD card is mounted as portable - Samsung (in one of the very few decisions they made correctly, in my opinion), opted to not allow adoptable storage - so the next won't apply.
2. If it's not a Samsung or LG, and the card was formatted as adoptable storage (or internal storage), there's no difference. Logically, the SD card is just added to the internal storage. So you can't tell the difference because there is none.
3. If it's a Samsung or LG, "Local Storage>Device Storage" is the apps name for what you're looking at. Use an app like
ES File Explorer to see where a file actually is. It shows the file structure, like Explorer does in Windows. So you can see if the file is on sdcard, internal, or extSdCard, the SD card. (You have no way of knowing what some file managers are showing you - "Files" may be all files, internal and SD card, shown as a single block. That's up to the developer. ES File Explorer (or
Total Commander) shows where any given file actually is. (If the phone is rooted, you can look ob /mnt for the SD card, then look in it for files
physically on the card. sd1 is the same place. (sd0 is internal storage.)
Or, you could install a terminal like
Terminal Emulator for Android and use ls to look for files directly from the Linux kernel of the phone. (You won't see apps unless the phone is rooted, but you will see pictures, videos, text files, anything you've stored, or caused to be stored, on the phone.)
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